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EDITED B Y 

Henry C. Lee and R. E. Gaensslen 





Advances 

in 

Fingerprint 

Technolo 



Henry C. Lee and R. E. Gaensslen 

Fingerprints constitute one of the most important categories of physical 
evidence, and one of the few in which true individualization is possible. 
During the last two decades, many new and exciting developments 
have taken place in the field of fingerprint science, particularly in the 
realm of methods for developing latent prints and in the growth of 
imaging and AFIS technologies. This fully updated Second Edition of 
the bestseller. Advances in Fingerprint Technology, covers major 
developments in latent fingerprint processing, including physical, 
chemical, instrumental, and combination techniques. Written by a 
renowned group of leading forensic identification and criminalistics 
experts, this valuable work presents exciting progress in fingerprint 
technologies, and in fingerprint comparison and identification. 



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CRC PRESS | 1 




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Advances 

in 

Fingerprint 

Technology 



SECOND EDITION 



CRC SERIES IN FORENSIC AND POLICE SCIENCE 



BARRY A. J. FISHER, Series Editor 
L.A. County Sheriff's Department 




TECHNIQUES OF CRIME SCENE INVESTIGATION 
Sixth Edition 

Barry A. J. Fisher 

SCIENTIFIC EXAMINATION OF QUESTIONED DOCUMENTS 

Revised Edition 

Ordway Hilton 

ADVANCES IN FINGERPRINT TECHNOLOGY 
Second Edition 

Henry C. Lee 
R. E. Gaensslen 

INSTRUMENTAL DATA FOR DRUG ANALYSIS 
Second Edition, Volumes 1-4 
Terry Mills, III 
J. Conrad Roberson 

INSTRUMENTAL DATA FOR DRUG ANALYSIS 
Second Edition, Volume 5 
Terry Mills, III 
J. Conrad Roberson 
H. Horton McCurdy 
William H. Wall 

INSTRUMENTAL DATA FOR DRUG ANALYSIS 
Second Edition, Volumes 6-7 
Terry Mills, III 
J. Conrad Roberson 
William H. Wall 
Kevin L. Lothridge 
William D. McDougall 
Michael W. Gilbert 



Advances 

in 

Fingerprint 

Technology 



SECOND EDITION 



EDITED BY 

Henry C. Lee and R. E. Gaensslen 




CRC Press 

Boca Raton London New York Washington, D.C. 



Library of Congress Cataloging-in-Publieation Data 



Advances in fingerprint technology / edited by Henry C. Lee, R.E. Gaensslen.— 2nd ed. 
p. cm — (CRC series in forensic and police science) 

Includes bibliographical references and index. 

ISBN 0-8493-0923-9 (alk. paper) 

1. Fingerprints. 2. Fingerprints— Data processing. I. Lee, Henry C. II. Gaensslen, R. E. 
(Robert E.) III. Series. 

HV6074 .A43 2001 
363.25'8— dc21 

2001025816 



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Preface 



The first edition of this book was published as a volume in the Elsevier Series 
in Forensic and Police Science. Elsevier’s book business has since been 
acquired by CRC Press LLC and CRC has supported and extended their 
forensic science program. We thank CRC for the opportunity to revise 
Advances in Fingerprint Technology to this second edition. 

Fingerprints is an area in which there have been many new and exciting 
developments in the past two decades or so, although advances in DNA 
typing have tended to dominate both the forensic science literature and 
popular information about advances in forensic sciences. Particularly in the 
realm of methods for developing latent prints, but also in the growth of 
imaging and AFIS technologies, fingerprint science has seen extraordinary 
breakthroughs because creative applications of principles derived from phys- 
ics and organic chemistry have been applied to it. 

Fingerprints constitute one of the most important categories of physical 
evidence. They are among the few that can be truly individualized. Fingerprint 
individuality is widely accepted by scientists and the courts alike. Fately there 
have been some modest challenges to whether a firm scientific basis exists 
for fingerprint individuality, based on the U.S. Supreme Court’s 1993 Daubert 
v. Merrell Dow Pharmaceuticals, Inc. decision [113 S.Ct. 2786 ( 1993) ] in which 
new standards for the admissibility of scientific evidence were articulated for 
the first time. The issues underlying these challenges are treated in Chapters 9 
and 10. A perspective on the history and development of fingerprinting and 
the fundamentals of latent print identification are treated in Chapters 1 and 
2, revised from the first edition. Patent fingerprint residue chemistry, on 
which every latent print detection technique is ultimately based, is covered 
in detail in a new Chapter 3. Chapter 4, the survey of latent print develop- 
ment methods and techniques, has been revised and updated. Chapter 5 on 
ninydrin analogues has been revised and updated. New chapters on physical 
developers (Chapter 7) and photoluminescent nanoparticles (Chapter 6) are 
added. AFIS system technology and fingerprint imaging are now widespread 
and may be considered mature. They are covered in a new Chapter 8. 





The first edition of this volume was dedicated to the memory and lifetime 
work of Robert D. Olsen, Sr., who wrote the original Chapter 2, but passed 
away unexpectedly before the book could be published. That chapter has 
been revised and retained in this edition. 

We want to thank all the contributors to this revised edition for their 
outstanding work and cooperation in bringing this work to completion. We 
also thank the staff at CRC, especially our acquisitions editor, Becky Me 
Eldowney, for making the task comparatively painless. Again we thank our 
wives, Margaret and Jacqueline, for their continued love and patience with 
us and our work habits. 




Acknowledgments 



We gratefully acknowledge the assistance of Ms. Nancy Folk, Ms. Cheng 
Sheaw-Guey, Mr. Hsieh Sung-shan, and Mr. Kenneth Zercie in the prepara- 
tion of the original Chapter 3 of the first edition. We particularly thank Ms. 
Erin Gould, a M.S. graduate of the University of Illinois at Chicago forensic 
science program, for her significant help with revised Chapter 4 for this 
present edition. We also thank Robert Ramotowski of the U.S. Secret Service 
Forensic Services Division for helpful commentary on and additional infor- 
mation for the revised Chapter 4. 





Contributors 



Joseph Almog, Ph.D. 

Casali Institute of Applied Chemistry 
Hebrew University of Jerusalem 
Jerusalem, Israel 
almog@vms.huji.ac.il 

John Berry, FFS, BEM 

Fingerprint Examiner and Historian 
(Retired) 

South Hatfield, Hertfordshire, England 

Antonio Cantu, Ph.D. 

Forensic Services Division 
U.S. Secret Service 
Washington, D.C. 
acantu@usss.treas.gov 

R. E. Gaensslen, Ph.D. 

Forensic Science, College of Pharmacy 
University of Illinois at Chicago 
Chicago, Illinois 
reg@uic.edu 

Robert J. Hazen 

Spotsylvania, Virginia 

Anil K. Jain, Ph.D. 

Department of Computer Science 
and Engineering 
Michigan State University 
East Lansing, Michigan 
jain@cse.msu.edu 



James L. Johnson 

Forensic Services Division 
U.S. Secret Service 
Washington, D.C. 

Henry C. Lee, Ph.D. 

Connecticut State Police Forensic 
Science Laboratory 
Meriden, Connecticut 

E. Roland Menzel, Ph.D. 

Center for Forensic Studies 
Texas Tech University 
Lubbock, Texas 

menzel@tomserver.phys.ttu.edu 

Sharath Pankanti 

IBM T. J. Watson Research Center 
Hawthorne, New York 
sharat@watson.ibm.com 

Clarence E. Phillips 

Robert Ramotowski 

Forensic Services Division 
U.S. Secret Service 
Washington, D.C. 
rramotowski@usss.treas.gov 



David A. Stoney, Ph.D. 

McCrone Research Institute 
Chicago, Illinois 

and Clinical Professor Forensic Science 
University of Illinois at Chicago 
Chicago, Illinois 
dstoney@mcri.org 





Table of Contents 



Preface 

Acknowledgments 
The Editors 
Contributors 

1 History and Development 
of Fingerprinting 

John Berry and David A. Stoney 



2 Identification of Latent Prints 

Robert D. Olsen, Sr. and Henry C. Lee 

3 Composition of Latent Print Residue 

Robert S. Ramotowski 

4 Methods of Latent Fingerprint Development 
Henry C. Lee and R. E. Gaensslen 

5 Fingerprint Development by Ninhydrin 
and Its Analogues 

Joseph Almog 



6 Fingerprint Detection with 

Photoluminescent Nanoparticles 



E. Roland Menzel 



7 Silver Physical Development 
of Latent Prints 

Antonio Cantu and James L. Johnson 

8 Automated Fingerprint Identification 
and Imaging Systems 

Anil Jain and Sharath Pankanti 

9 Measurement of Fingerprint Individuality 
David A. Stoney 

10 The Expert Fingerprint Witness 
Robert J. Hazen and Clarence E. Phillips 



History and Development 
of Fingerprinting 

JOHN BERRY 
DAVID A. STONE Y* 




Contents 



Introduction 

Evolution and the Elliptical Whorl (1976) 

Neolithic Bricks (7000 B.C.) 

Prehistoric Carvings (3000 B.C.) 

Mummies 

Finger Imprints on Artifacts in Antiquity (circa 3000 B.C.) 
Grauballe Man (A.D. 400) 

Philosophical Transactions (1684) 

De Externo Tactus Organo (1686) 

William of Orange (1690) 

Thomas Bewick (1753-1828) 

Concerning the External Physiological Examination of the 
Integumentary System (1823) 

Fingerprint Classification 

Dr. Ivan Vucetich (1858-1925) 

The Henry System 

Sir Edward Henry and Sir William Herschel 
Dr. Henry Faulds (1843-1930) 

Sir Francis Galton (1822-1911) 

Early Fingerprint Usage in Other Countries 
Germany 
Cuba 
Canada 

Australia and New Zealand 
United States of America 
Developments to Date 
Reference 

Addendum to the First Edition 
Update 




Introduction 



The fascinating story of the development and use of fingerprints in the last 
hundred years will only be properly appreciated if the reader is acquainted 
with some knowledge of dactyloscopy; therefore I will briefly outline the 
basic details of this science. The inside surfaces of the hands from fingertips 
to wrist and the bottom surfaces of the feet from the tip of the big toe to the 
rear of the heel contain minute ridges of skin, with furrows between each 
ridge. A cross section of a finger would look exactly like the cross section of 
a plowed field. Whereas on a plowed field the ridges and furrows run in 
straight parallel lines, on the hands and feet the ridges and furrows frequently 
curve and, especially on the fingertips and toe ends, the ridges and furrows 
form complicated patterns. The ridges have pores along their entire length 
that exude perspiration; hence, when an article is picked up, the perspiration 
runs along the ridges and leaves an exact impression of the ridges, just as an 
inked rubber stamp leaves its impression on a blank sheet of paper. 

Ridges and furrows have evolved on the hands and feet to fulfill three 
specific functions: 

1. Exudation of perspiration 

2. Tactile facility 

3. Provision of a gripping surface 

The ridges and furrows form seven basic characteristics, as shown in 
Figure 1.1. Some authorities consider that only two types of characteristics 





Figure 1.2 Basic fingerprint patterns. 

are present, a ridge ending and a bifurcation, all other characteristics being 
variations of the two basic forms. I consider that my illustration defines the 
most important varieties of ridge detail, also known as ridge characteristics. 

The ridges and furrows form patterns on the last joint of the fingers and 
toes, forming four basic types, as shown in Figure 1.2. There are variations 
of these patterns, especially with whorls, but these are the province of the 
fingerprint expert. Every person in the world shares these patterns — a 
person can have all of one type or even a mixture of all of them. The everyday 
use of fingers as an identification method and the production of finger and 
palm evidence in courts of law are based on one magnificent premise: no 
one has ever been found who has a sequence of ridge detail on the hands 
and feet that is identical to the ridge detail of any other person. 



Evolution and the Elliptical Whorl (1976) 

Before I researched the history of fingerprints in 1975, the earliest evidence 
of ridge detail on the hands and feet of humans was seen in the 4000-year- 
old mummies of ancient Egypt. The hands and feet of mummies have been 
examined on numerous occasions, and I can confirm the presence of ridge 
detail on the mummies’ digits. Before 1975, the only other evidence reported 
was the presence of a small portion of palm imprint on hardened mud found 
in Egypt on a paleolithic site at the Sebekian deposit, Kom Ombo plain, on 
the east bank of the river Nile, dated around 10,000 years ago. The fact that 
primates have ridge detail was announced for the first time, as far as I can 
discover, by Joannes Evangelista Purkinje in his thesis (discussed later) pub- 
lished on December 22, 1823. He wrote: 



In the hands of the monkeys, as well as in their prehensile tails, similar lines 
occur, the distinction of which adds to the knowledge of the characteristics 



of all species. Zoologists, unless they consider them unimportant, will add 

further details. 

Purkinje illustrated a palm impression and a small portion of the prehensile 
tail of a spider monkey. 

In 1975-1976, 1 and my colleagues in the Fingerprint Office in Hertford- 
shire, U.K. — Roger Ball, David Brooker, Nicholas Hall, Stephen Haylock, 
and Martin Leadbetter — commenced protracted research to confirm that 
all species of primates have ridge detail on their hands and feet in patterns 
and toe ends that conform to human patterns (see Figure 1.2). We prepared 
a list of over 180 species of primates from the tree shrews (family Tupaiidae) 
to the gorilla (family Pongidae) and prepared a roster whereby, in small 
groups, we visited zoos and private collections, examining and in many cases 
taking impressions of the hands and feet of primates. This research engen- 
dered publicity in the press and television; one sarcastic writer commented 
in a national newspaper that Stephen Haylock was fingerprinting monks. 

Eventually, Leadbetter and I contacted Professor and Mrs. Napier, who 
have now retired to a Scottish island. Professor Napier was a professional 
writer and a world-renowned expert on the hand; his wife Prue was also a 
writer and worked in the British Natural History Museum on Cromwell Road, 
London. We discovered that her terms of reference covered a section of the 
museum denied to ordinary visitors where thousands of deceased primates, 
many of them stuffed with straw, were placed in wide receptacles in an air- 
conditioned hall. Mrs. Napier explained that a “rule” existed whereby when 
a primate died in England, the skin was sent to the museum. This “rule” has 
been in existence for many years. For example, Roger Ball and I used a 
fingerprint-lifting technique to obtain the entire length of ridge detail from 
the prehensile tail of a red howler monkey that had died in 1829. Figure 1.3 
shows an enlarged section of the lift. 

The museum authorities gave permission for Roger Ball, Stephen Hay- 
lock, Martin Leadbetter, and me to examine all the stuffed primates in the 
huge collection. Working in pairs and using our vacation days, we eventually 
examined the hand and foot surfaces of all the primates. In a few instances 
we lifted ridge details from the hands and feet of selected specimens. This 
was done by carefully smoothing several layers of acrylic paint over the 
surfaces and waiting for each layer to dry before peeling it off. When we 
returned to the Fingerprint Office in Hertfordshire, the acrylic lifts were 
dusted with aluminum powder and then lifted with transparent tape and 
placed on transparent Cobex, forming a negative duly processed in the 
Camtac machine, producing a positive impression, i.e., ridges were black and 
furrows and pores were white. After 18 months of research, we had become 




Figure 1.3 Portion of the prehensile tail of a red howler monkey (1829). 



the first researchers, as far as I can ascertain, to examine and record the hands, 
feet, and prehensile tails of every species of primate. 

In a later section, I shall discuss the fingerprint pioneer Dr. Henry Faulds 
(pronounced “folds”) in some detail; but in the present context I believe it 
is enormously interesting to report that on February 15, 1880, Faulds wrote 
to evolutionist Charles Darwin requesting his aid in obtaining the finger 
impressions of lemurs, anthropoids, etc. “with a view to throw light on 
human ancestry.” On April 7, 1880, Darwin replied to Faulds: 

Dear Sir, 

The subject to which you refer in your letter of February 15th seems to 
me a curious one, which may turn out interesting, but I am sorry to say 
that I am most unfortunately situated for offering you any assistance. I live 
in the country, and from weak health seldom see anyone. I will, however, 
forward your letter to Mr. F. Gabon, who is the man most likely that I can 
think of to take up the subject and make further enquiries. 

Wishing you success, 

I remain, dear Sir, 

Yours faithfully, 

Charles Darwin 



The “Mr. F. Galton” referred to in the letter from Darwin in due course 
became an authority on fingerprint matters in England and was part of an 
establishment clique that sought to revile Faulds (to be described later). 
However, note the amazing chain of events: . . . fingerprint pioneer Faulds . . . 
primates’ fingerprints . . . Charles Darwin . . . Mr. F. Galton (later Sir Francis 
Galton) . . . fingerprint pioneer! 

During the summer of 1976, 1 was, as always, fully occupied in my work 
as a fingerprint expert in Hertfordshire, specializing in searching for the 
ownership of finger imprints found at crime scenes, known in the U.S. by 
the particularly apt expression “cold searching.” Many identifications are 
made as the direct result of suspects being named by investigating police 
officers, but it is thrilling for a fingerprint expert, even a grizzled veteran like 
myself working with fingerprints for 37 years, to delve into the unknown and 
give the police a named person for the crime they are investigating, a name 
completely fresh and unknown to them, which we refer to as being “out of 
the blue.” Some astute detectives, when given the name as the result of a 
successful search, attempt to give the impression that somehow “they had an 
idea” that the name supplied to them was at that time under serious review. 
Fingerprint experts do not like this because the identification might have 
been made after laboriously searching perhaps thousands of fingerprint 
forms. 

So in 1976 my position was that I had been scanning hundreds, possibly 
thousands, of fingerprints every working day for almost 22 years and at the 
back of my mind was the ever-present thought that all primates have “human 
type” finger impressions — after all, we are all primates — and, prompted 
by the letter from Faulds to Darwin, some original thoughts occurred to me. 

I had recently read Prue Napier’s book Monkeys and Apes, wherein she 
illustrated every primate, describing the physical similarities and differences 
that occur in geographically separate areas, such as South America (only 
South American primates have ridge detail on their prehensile tail strip), 
Japan, Africa, Sumatra, Gibraltar, India, and Madagascar. I perused books 
on plate tectonics, averaging the estimated dates of the separation of Mada- 
gascar from the East African coast, and calculated that this occurred 
50,000,000 years ago. Madagascan primates, I mused, differ physically from 
African primates, but they also bore ridge detail on their hands and feet. One 
fingerprint pattern that frequently occurs on primates in all geographical 
areas is the elliptical whorl (Figure 1.4), which is also found on human finger 
impressions. I must stress that arches, tents, loops, and whorls (see Figure 1.2) 
are also found on primates, but I “latched onto” the elliptical whorl as the 
basis for my sudden inspiration. Surely, if East African and Madagascan 
primates have elliptical whorls (among other patterns), only two theories 
could account for this phenomenon: 



Figure 1 .4 Elliptical whorl. 

Theory 1: Before the distribution of certain land masses between 
50,000,000 and 100,000,000 years ago, ridge detail was present on the 
hands and feet of our subprimate ancestors. 

Theory 2: At some undetermined moment in time, perhaps allied with 
the emergence of Homo sapiens, primates all over the world suddenly 
developed ridge detail on their hand and foot surfaces, all species 
having associated patterns. 

I submit that Theory 2 does not even require the remotest consideration, 
unless one is prepared to put forward a subtheory of Divine Intervention; 
but even then, cynically, why would God suddenly decide to gratuitously 
hand out ridge detail? I forwarded details of Theory 1 to Professor Napier 
and to Professor Beigert, Zurich, Switzerland, for their consideration. I met 
with Professor Napier, who kindly presented copies of his relevant publications. 

In Monkeys Without Tails, Professor Napier considers that the develop- 
ment of tree climbers like Smilodectes required, among other physical devel- 
opments, “replacement of sharp claws by flattened nails associated with the 
development of sensitive pads on the tips of the digits.” He wrote to me: 

I am quite sure that fingerprints are as old as you suggest, particularly if 
the evolution of the monkeys is put back to the Eocene. The chances of 
evolving the “human” primate pattern are very high by means of the simple 
process of evolutionary convergence which your thesis strongly suggests . . . 
it is obviously a basic pattern of Nature. 




For many years Professor Beigert has published numerous books con- 
cerning ridge detail on the hand and foot surfaces of selected primates. He 
also forwarded to me copies of his literature and wrote, making the following 
observations: 

I agree with you that dermatoglyphics on palma and planta of primates 
have to be dated very early. In my opinion in the Paleocene, 50,000,000- 
60,000,000 years ago. 

In his book The Evaluation of the Skull, Hands and Feet for Primate 
Taxonomy (1963), Professor Beigert writes: 

Much less attention has been given to the fact that among the other sense 
organs, the touch receptors underwent a significantly higher development. 

My thesis was published in Fingerprint Wlwrld (July 1976) and in my 
esoteric annual publication Ridge Detail in Nature (1979); both publications 
were circulated to fingerprint bureaus, universities, and museums all over 
the world. No one has claimed prior publication of my theory regarding the 
fact that subprimates bore ridge detail before the separation of land masses. 

I therefore submit that ridge detail appeared on the hands and feet of 
our subprimate ancestors over 100,000,000 years ago (a new 1987 estimate 
for the separation of Madagascar from Africa is closer to 200,000,000 years) 
and that our subprimate ancestors developed ridge detail on their hands and 
feet to facilitate the evolutionary requirement for grip, tactile facility, and the 
exudation of perspiration. 



Neolithic Bricks (7000 B.C.) 

Dame Kathleen Kenyon carried out excavations in the ancient city of Jericho, 
and in her book Archaeology of the Holy Land, referring to houses dated 
between 7000 B.C. and 6000 B.C., she reported 

The bricks of which the walls were constructed were made by hand (not in 
moulds, as is usual later), in shape rather like a flattened cigar, with the 
surface impressed with a herringbone pattern by pairs of prints of the brick- 
layer’s thumbs, thus giving a keying such as is provided by the hollow in 
modern bricks. 

In Paphos — History and Archaeology by F. G. Maier and V. Karageorghis, 
dealing with excavations in Paphos, birthplace of Aphrodite, reference is 
made to the walls of the ancient city, eighth century B.C. 





The bricks, carefully laid and accurately jointed, are of near uniform size 
and of dark brown clay. A distinctive bright red-clay mortar was used. Many 
bricks have impressed fingerprints on their lower side. 



Prehistoric Carvings (3000 B.C.) 



Recently I discovered details on two archaeological items that proved to my 
entire satisfaction that early humans were cognizant of patterns on their 
fingertips. However, before discussing them, I wish to report on the work of 
“a distinguished fingerprint authority,” a certain Mr. Stockis, who published 
a treatise in the early 1920s in which he attempted to justify his claims that 
persons who carved patterns on standing stones in dolmen on Goat Island, 
Brittany, France, were aware of ridge detail on their digits. The carvings he 
illustrated depicted symbolic arches, tents, loops, and whorls. 

The so-called Stockis theory was investigated by the eminent fingerprint 
expert Professor Harold Cummins, from the U.S., who reported 

If it be true that Neolithic men really noted fingerprint patterns, and with 
the attention to minute detail which is claimed, credit is due to them for a 
spontaneous interest and keenness in such observation hardly matched by 
the average man of the present day. 

In his critique of the Stockis theory, Professor Cummins acknowledges that 
pottery making could have revealed ridge detail to Neolithic humans and 
accepts that the carvings are “highly suggestive” of fingerprints; he even 
concedes that this could have been associated with hand worship. However, 
he concludes that although ridge detail can be noted in the carvings, there 
are other features included that definitely do not refer to dermatoglyphics. 
He concluded that “sound evidence that the carved designs had their origin 
in fingerprints appears to be wanting.” 

The first of my discoveries concerns a national monument at New 
Grange, Republic of Ireland (Eire), that I wrote about in the 1984 edition of 
Ridge Detail in Nature: 

The national monument at New Grange dates from around 3,000 B.C. and 
features a huge man-made mound with a narrow passage leading to an 
inner burial chamber. An opening is located above the entrance so that for 
just a few moments at dawn on 21st December each year the rays of the 
rising sun penetrate along the passage to illuminate the burial chamber. A 
postage stamp issued on 4th May 1983 depicts patterns at the monument 
incised in stone. I note that the four basic fingerprint patterns are shown, 
together with numerous deltas. Is it mere coincidence that these patterns 





Figure 1 .5 Standing stone, Goat Island. (Redrawn by John Berry, from The Mega- 
lithic Builders of Western Europe, Glyn Daniel, 1963.) 



are found on the design, or was the interest of a pre-Celtic artist kindled 
by a perusal of his fingerprint patterns? 



In Ridge Detail in Nature (1986) I illustrated and described for the first time 
in a ridge detail context a carving on a standing stone on Goat Island 
(Figure 1.5). I wrote: 



Megalithic tombs and architectural monuments were built in Western 
Europe around 4,000 years ago, and the richest carvings are found in Brit- 
tany, north western France. It is thought that inspiration for the remarkably 
decorated tombs came from Spain and Southern France. A dozen charac- 
teristic symbols on the tombs represented important items in the lives of 






the megalithic builders, including axeheads, horns, yokes, the sun, etc. This 
photograph of carvings from Gavrinnis is covered with symbolic represen- 
tations, and the seemingly superimposed shape at the bottom of the carving 
shows a tent pattern. Ridge detail is scarce, but pores are quite clear on the 
ridges, being especially noticeable on the ridges draped over the central 
spine. I have no doubt that this particular carver was aware of patterns on 
finger tips, possibly superimposing one of his own patterns, as clear and 
precise as any of English wood-carver Thomas Bewick’s fingerprint repre- 
sentations. (Bewick is discussed later.) 

I do accept there is the slight possibility that the New Grange designs 
could be coincidental, although I do believe that the artist was conversant 
with patterns plainly visible on the ends of his fingers or the fingers of his 
associates; but I certainly do not have any doubts whatsoever that the person 
who carved the tent pattern (see Figure 1.5) was aware of fingerprint patterns. 
This megalithic monument, carved in France at about the same time as the 
pyramids were being built, convinces me that the artisan knew of this pattern, 
and possibly, to accord individuality to one of his designs, he incorporated 
one of his digit patterns, perhaps carved from a mud impression purposely 
made. The tent pattern is “squared-off” at the base. The sweat pores are 
pronounced, equally spaced on the ridges; I regard this as being a most 
significant pointer. This carving of a tent pattern was not a coincidence: it 
was carved from direct observation. I unhesitatingly align myself with, and 
fully support, the Stockis theory. 



Mummies 



As I have stated, the examination and recording of ridge detail on the hands 
and feet of mummies has been reported. I have visited museums in several 
countries, always specifically seeking out the Egyptian sections, and although 
many of the mummies were wrapped, I have been able to scrutinize ridge 
detail on the hands and feet of embalmed bodies on display and confirm the 
presence of fingerprint patterns similar to those shown in Figure 1.2. 

In 1977, the mummy Asru, from the Temple of Karnak, was fingerprinted 
by experts in Manchester under the direction of Detective Chief Inspector 
Thomas Fletcher, head of the Fingerprint Bureau of the Greater Manchester 
Police. He kindly sent me a report and illustrations that were subsequently 
published in Fingerprint Whorld. Mr. Fletcher utilized the technique I have 
already described when the Hertfordshire personnel fingerprinted primates: 
the application of layers of acrylic paint on the digits. (This technique was 
invented by Roger Ball and was revealed for the first time in Fingerprint 
Whorld, January 1976.) Mr. Fletcher used his experience as a detective to 



discover the occupation of Asm in the Temple of Karnak; she was either a 
dancer or a chantress: 

Three thousand years ago Egyptian temple dancers performed their ritual 
dances barefoot, the foot being used as part of the body’s expression. The 
sole was in constant contact with the ground and even on the smoothest of 
flooring there would be friction and consequent wearing of the ridges on 
the underside of the toes and balls of the feet. Asru’s feet did not show any 
traces of this constant contact with the floor, the depth of the furrows and 
the clarity of the characteristics were not consistent with her having been 
a dancer, and the alternative of her being a chantress was much more 
acceptable. 



Finger Imprints on Artifacts in Antiquity (circa 3000 B.C.) 

In Fingerprint Whorld, October 1976, 1 published my research on this subject 
under the rather facetious title “Potter Throws Light on Prints.” I consider 
that I covered the subject quite fully and wrote: 

Research into finger imprints in antiquity is a fascinating subject, because 
references occur of fingerprints on pottery and figurines in many parts of 
the world, even in pre-history. The scope for detailed research by the fin- 
gerprint expert is considerable, because my initial source material (quoted 
later) reveals authorities finding fingerprints on Neolithic vases, Bronze Age 
cooking pots, Assyrian clay tablets, ancient Mexican pottery and Aztec clay 
figures. Obviously, many of these instances occurred in the manufacture of 
articles where the manipulation of the basic clay into utensils indirectly left 
fingerprints. I write here detailing examples which suggest that the finger- 
prints were purposely indented into the clay. The earliest trace of finger 
imprints being purposely impressed occurred in Mesopotamia and dates 
from circa 3,000 B.C. where an authority asserts that a “digital impression” 
was placed on each brick used in the construction of the king’s storehouse. 

This method of making identifying marks is also found on bricks used in 
the construction of the “royal buildings” in Ancient Egypt. It is pertinent 
to note that in these two examples the buildings were for kings or pharaohs, 
suggesting the importance placed in the craftsmanship which was confirmed 
by the finger impressions of the masons. 

William Frederick Bade, once director of the Palestine Institute of 
Archaeology, conducted excavations at various sites in Palestine and at one 
place found finger imprints on many pieces of broken pottery. The chaotic 
state of this scene caused initial difficulty in dating artifacts, but it transpired 
that a study of the imprints on the numerous shards indicated that one potter 





made most of them. These “identifications” permitted the confused debris 
to be dated accurately; in fact, this particular excavation was dated to the 
fourth century A.D. Commenting on this case, Fingerprint Magazine (1937) 
stated that “these impressions were obviously intentional, and, no doubt, 
represented the workman’s individual trade mark.” 

A Chinese clay seal, dated before the third century B.C., has been the 
focus of considerable research and speculation for many years. A left thumb 
imprint is deeply embedded in the seal, and on the reverse side is ancient 
Chinese script representing the name of the person who made the thumb 
imprint. The mark is so specific in pressure and placing that there can be no 
doubt that it was meant as an identifying mark. If this is so, there is the strong 
inference that the Chinese were aware of the individuality of fingerprints well 
over 5000 years ago. 

According to Mr. Laufer, a famous researcher who worked at the Field 
Museum of Natural History in the U.S., before the first century B.C., clay 
seals were used extensively in sealing documents such as official letters and 
packages. Of the superb left thumb imprint mentioned above, he stated: 

It is out of the question that this imprint is due to a mere accident caused 
by the handling of the clay piece. This impression is deep and sunk into the 
surface of the clay seal and beyond any doubt was effected with intentional 
energy and determination. In reasoning the case out logically, there is no 
other significance possible than that the thumb print belongs to the owner 
of the seal who has made his name on the reverse side. This case is therefore 
somewhat analogous to the modern practice of affixing on title deeds the 
thumb print to the signature, the one being verified by the other. This 
unique specimen is the oldest document so far on record relating to the 
history of the fingerprint system. 

There is no evidence to conclude that the ancient Chinese were aware of 
the individuality of fingerprints on a universal basis. However, the care taken 
to impress the clay seals suggests that the persons utilizing this form of 
signature (even should they only be symbolic tokens, as suggested) were 
aware that the design on their fingers or thumbs so applied constituted 
individuality. This must represent, even at its crudest level, the local recog- 
nition that the person who impressed a digit on a seal was permanently 
bound to the contents of the documents so certified. 

A researcher who dedicated many years of work in this direction, 
although he was not a fingerprint expert, stated: 

Fingerprint identification in our usage of the term appears to have been 
practiced in a simple form in times long past . . . but the history of fingerprint 
identification becomes shadowy as it is traced backwards. 




I have examined Roman pottery and noted that finger imprints are 
sometimes present; one example in my possession shows three whorl types 
(twin loops) on the semismoothed underside. Yet when I was in Romania in 
1985, 1 visited the ruins of a Greek settlement at Hystria, on the western coast 
of the Black Sea, and found shards of pottery completely devoid of finger 
imprints. I was extremely pleased to find the handle and part of the side of 
a Getic earthenware vessel among the rubble on the site. It was made during 
the first century B.C., and under examination with my fingerprint magnifying 
glass, I could see that the handle and side had been smoothed with fingers 
so finely that I believe every endeavor had been made to avoid leaving finger 
imprints on the finished product. I visited museums in Hystria, Constantsa, 
and Bucharest, especially looking for finger imprints on pottery, and did not 
even find a lone example. Ergo, it is reasonable to assume that the potters in 
this area at least decided it was worthwhile removing offending imprints, 
which they had noted, in order to obtain an unsullied surface, a rather civilized 
artistic appreciation of subtlety of form. 



Grauballe Man (A.D. 400) 

On Saturday, April 26, 1952, a body was discovered in the Nebelgard Fen 
near Grauballe, in Jutland, and 14 C dating revealed that the body had been 
in the bog between A.D. 1 and A.D. 400. The skin had been tanned like leather 
owing to the preservative qualities of the bog water. The cause of death was 
a deep incision across the throat, and it was presumed that the man had been 
ritually sacrificed to a fertility god to ensure the survival of his fellows. Two 
members of the staff of the police laboratory at Aarhus were entrusted with 
the examination of the Grauballe man’s hands and feet. They found the ridge 
detail was excellent and were able to take impressions from the body. The 
right thumb was “a double curve whorl,” a twin loop, and the right forefinger 
was an ulnar loop. 



Philosophical Transactions (1684) 

The first person to study and describe ridges, furrows, and pores on the hand 
and foot surfaces was English plant morphologist Nehemiah Grew 
(Figure 1.6), born in Warwickshire in 1641. He was the first fingerprint 
pioneer; besides writing on the subject, he also published extremely accurate 
drawings of finger patterns and areas of the palm. In the 1684 publication 
he described, in the most beautiful phraseology, descriptions and functions 
of ridge detail: 



Figure 1.6 Nehemiah Grew. (Drawn by John Berry.) 

For if any one will but take the pains, with an indifferent Glass, to survey 
the Palm of his Hand very well washed with a Ball; he may perceive (besides 
those great Lines to which some men have given Names, and those of middle 
size call’d the Grain of the skin) innumerable little Ridges, of equal bigness 
and distance, and everywhere running parallel with one another. And espe- 
cially, upon the ends and first Joynts of the Fingers and Thumb, upon the 
top of the Ball, and near the root of the Thumb a little above the Wrist. In 
all which places they are regularly disposed into Spherical Triangles, and 
Ellipticks. Upon these Ridges and Pores, all in Even Rows, and of that 
magnitude, as to be visible to a very good Eye without a Glass. But being 
viewed with one, every pore looks like a little Fountain, and the sweat may 
be seen to stand therein, as clear as rock water, and as often as it is wiped 
off, to spring up within them again. That which Nature intends in the 
position of these Ridges is, That they may the better suit with the use and 
motion of the Hand: those of the lower side of every Triangle, to the bending 
in or clutching of the Fingers: and those of the other two sides, and one of 
the Ellipticks to the pressure of the Hand or Fingers ends against any body, 
requiring them to yield to the right and left. Upon these Ridges, the Pores 
are very providently placed, and not in the furrows which lie between them; 
that so their structure might be more sturdy, and less liable to be depraved 
by compression; whereby only the Furrows are dilated or contracted, the 
Ridges constantly maintaining themselves and so the Pores unaltered. And 
for the same reason, the Pores are also very large, that they may be still 




better preserved, tho the skin be never so much compressed and condens’d by 
the constant use and labour of the Hand. And so those of the Feet, notwith- 
standing the compression of the skin by the weight of the whole body. 



Grew died suddenly on March 25, 1712. He is buried at Cheshunt Parish 
Church, Hertfordshire. 



De Externo Tactus Organo (1686) 

Grew’s contemporary, Marcello Malpighi (1628-1694), also a plant morphol- 
ogist, researched the functions of the human skin, and the “Malpighian 
layers” were named for him. He worked at the University of Bologna, Italy, 
and in his publication he mainly dealt with the skin, although he did briefly 
mention ridge detail. It is believed that Grew and Malpighi corresponded to 
a degree, but the differences in language were a frustration, strangely because 
Grew was more adept at Latin usage than the Italian. 



William of Orange (1690) 

I am sure that the reader will think this section is a hoax, but I report herewith 
one well-known historical fingerprint landmark, and the latest tremendous 
1987 discovery, both having a direct connection with the expatriate Dutch 
monarch William of Orange. The city of Londonderry (now in Northern 
Ireland) was under siege until relieved by forces under the command of 
William of Orange, and in 1691, 225 citizens of Londonderry, who had 
suffered damage and loss during the siege, made a representation to London 
for compensation. The claimants appended digit impressions on the docu- 
ment, adjacent to their signatures, obviously considering the individuality of 
their fingers as being inviolable. I have examined a photograph of the doc- 
ument (and have tried really hard but unsuccessfully to trace the original) 
and report that the imprints are unfortunately of poor quality, but it must 
be remembered that they were made 300 years ago. 

An accidental fire occurred at the historic building Hampton Court, west 
of London, causing considerable damage; early in 1987, workmen removed 
some warped wooden panels in The Little Oak Room, Fountain Court, and 
found that the plaster underneath bore 17 complete handprints. I immedi- 
ately visited the site with Martin Leadbetter and Nicholas Hall, a Hertford- 
shire Constabulary photographer, and we made a detailed examination, 
including measurements, photography, and an abortive attempt at lifting. 






Figure 1.7 Right palm imprint in plaster, Hampton Court, London, 1689-1690. 
(Figure supplied by Nicholas John Hall, M.F.S., Hertfordshire.) 

Most of the handprints were excellent, revealing clear ridge detail; photograph 
A 2 (Figure 1.7) shows the finest example. The plaster was made of lime, sand, 
and animal hairs. Archaeologists told us that The Little Oak Room had been 
redecorated in 1689-1690 for King William III and his queen. The hands had 
been impressed in the plaster before it had hardened. We found that three 
different people had made the imprints. I do not believe that the plasterers 




Figure 1.8 Thomas Bewick. (Drawn by John Berry.) 

would desecrate their handiwork; perchance the vagrant handprints were 
made by carpenters, soldiers, or servants who would be aware that large wooden 
panels of oak would speedily be placed atop the plaster. It was a fascinating 
experience to have the opportunity to examine the handprints on the wall, albeit 
the results of our examination were officially handed to the Hampton Court 
authorities as part of the records of the archaeological and other finds before 
refurbishment; also, our work was featured in an official Home Office film that 
is scheduled for television broadcast and publication in book form. 



Thomas Bewick (1753-1828) 

Thomas Bewick (Figure 1.8) is mentioned quite frequently in fingerprint 
publications simply because in a few books he used an engraving of his 
fingerprints as a signature. The importance of this fact is that he did this almost 
200 years ago, and authorities such as Sir William Herschel have credited Bewick 
with stimulating their initial interest in the study of fingerprints. 

He was born in Ovingham, Northumberland, England, on August 12, 
1753, the son of a farmer. His early school career was marred by his absence 
from classes and disinterest in Latin, English grammar, and arithmetic, 
although he was eventually constrained to study them to a reasonable stan- 
dard, as one contemporary writer put it: 



By kindly words of persuasion a reformation was at length affected that 
severe discipline and punishment had failed to accomplish. 

He used all the spaces in his school papers to draw murals, and when he used 
these up he continued his artistic progress by chalking designs on gravestones 
and the church porch. He became famous in the rural community as an 
artist, and he decorated the walls of their cottages “with an abundance of my 
rude productions at a very cheap rate.” 

While still a child, his head was scalded and thereafter his crown had no 
hair, necessitating, when he grew older, the application of a brown silk cap. 
When he was 14 years old, he became an apprentice to an engraver in 
Newcastle, and after 5 years he completed his apprenticeship; the first book 
with a Bewick woodcut was published in 1774. 

As the years progressed, Bewick became famous throughout England, 
and ultimately his fame became worldwide. Without doubt he was England’s 
finest engraver. He invented the “white line” wood-engraving technique, 
“thus paying attention, not to what he left, but what he cut away from the 
block.” Most of his famous wood engravings featured animals and birds. His 
A General History of the Quadrupeds ran to eight editions, as did his monu- 
mental History of British Birds. The finger imprint in Figure 1.9, showing the 
cottage and trees etched faintly in the background, is from History of British 
Birds 1797-1804. His love of the countryside and nature must have caused 
him to note ridge detail on his hands. It has not been possible to find out 
how he concluded that ridge detail was unique, but it is obvious from his 
carved imprint superimposed with Thomas Bewick his Mark that he was 
utterly satisfied that his imprint denoted individuality. One of his contem- 
poraries observed that “Bewick’s signature is sometimes written, a genuine 
autograph, but generally printed; the quaint conceit of his thumb print is 
amusing.” Bewick died on November 8, 1828, at Gateshead, and he was 
buried in Ovingham churchyard, in the parish where he was born. 



Concerning the External Physiological Examination of the 
Integumentary System (1823) 

Joannes Evanelista Purkinje was a Bohemian, and part of his thesis published 
on December 22, 1823, dealt in considerable detail with the functions of 
ridges, furrows, and pores; additionally, he illustrated and described nine 
fingerprint patterns: one arch, one tent, two loops, and five types of whorl. 
In 1985 my Hertfordshire colleague Martin Leadbetter optimistically wrote 
to the Burser of Wroclaw University, Poland, asking for photographs and part 
of the original thesis dealing with fingerprints. In 2 months, to our considerable 




Figure 1.9 Trademarks of Thomas Bewick. (From the publications of Thomas 
Bewick. With permission.) 

surprise, a 35-mm film arrived with negatives of all the pertinent pages in 
Latin (Martin has entrusted the film to me to retain in my capacity as 
Historian of The Fingerprint Society). Professor Harold Cummins and 
Rebecca Wright Kennedy, of the U.S., translated the thesis in 1940, and The 
Royal Society of London obtained the translation and duly gave permission 
for it to be published in Fingerprint Whorld, April 1987. 

These are some of the interesting observations Purkinje made regarding 
the four basic patterns (Figure 1.2) and also a most detailed description of a 
palm impression: 

Arch: From the articular fold, rugae and sulci first course in almost straight 
lines transversely from one side of the phalanx to the other; then little 
by little they become more curved in the middle, until they are bent in 
arches which are nearly parallel with the periphery of the phalanx. 

Tent: This is almost the same conformation as the above, the only dif- 
ference being that the transversely coursing ridges are wrapped over 
a little perpendicular stria, as if it were a nucleus. 



Loop: Now if this oblique stripe by a simple curve returns to the side 
from which it came and follows many others in a similar curve, an 
oblique loop is formed which may be more or less erect or may bend 
forwards. Near its base, on one side or the other, a triangle is formed 
from the different directions of the rugae and sulci. Their configura- 
tion in the form of the oblique loop is the commonest, and I may 
almost say, typical of man. 

Whorl: The circle, where in the ellipse a simple line occupies the center, 
there is a small tubercle (island); it is surrounded with concentric 
circles which reach the rugae of the semicircular space. 

Palm: From the space between the index finger and the thumb, great 
numbers of parallel lines run which pass in diverging directions across 
the palm, next to the linea palmiformis, into the margins of the meta- 
carpals of the thumb and little finger. Thus triangles are formed with 
the vertices at the wrist. This is their most common conformation. 
Other parallel lines from the roots of the fingers meet and accompany 
the lines running across from the interval of the thumb and the index 
finger toward the external margin of the fifth metacarpal. Running 
out from these intervals, loops and whorls are interposed; but it would 
take too long to explain in this chapter the many varieties of these. 
On the thenar eminence, a trapezoidal region occurs where the rugae 
and sulci are set transversely to the circles. On the hypothenar emi- 
nence, toward the radial margin of the metacarpal, a larger loop is 
often observed where the rugae and sulci going out from the margin 
are again reflected onto it. Sometimes an elliptical whorl is seen on 
this eminence. 



Fingerprint Classification 

A major step forward in the use of fingerprints was a method of classification 
that enabled fingerprint forms bearing differing patterns to be placed in a 
certain order, thus enabling the search area to be minimized. If a classification 
system did not exist, and a person gave a wrong name, each set of fingerprint 
forms would have to be examined to discover the correct identity of the 
offender; the person would obviously not be traced by doing an alphabetical 
check. Many countries in the world now use the “Henry System,” the brain- 
child of Sir Edward Henry (Figure 1.10), an Englishman who served in India 
toward the end of the nineteenth century. His system became operational at 
Scotland Yard in 1901, but I must point out that a European who emigrated 
to Argentina in 1884 caused the world’s first fingerprint bureau to be insti- 
tuted in 1896. 




Figure 1.10 Sir Edward Henry. (Drawn by John Berry.) 



Dr. Ivan Vucetich (1858-1925) 

Dr. Ivan Vucetich (Figure 1.11) was employed in the Central Police Depart- 
ment, La Plata, Argentina, and was ordered to install the French Bertillon 
Anthropometric Identification System, which used a number of body mea- 
surements and was in extensive use in European countries. Vucetich obtained 
a copy of the journal Revue Scientific which contained an article on English 
fingerprint pioneer Francis Galton, who had formulated his own classifica- 
tion system. Dr. Vucetich became extremely interested in fingerprints and 
within a year had worked out his own unique system for classifying them. 
This became known as “vucetichissimo,” and it utilized four fingerprint pat- 
terns as described in his book Dactilospia Comparada. In 1893, the Rojas 
murder was solved by fingerprints, proving their effectiveness, and Vucetich 
was enthusiastically operating a fingerprint office built at his own expense. 
In 1893, he was suddenly ordered to abandon his fingerprint system and 
revert to bertillonage. Of course, he realized that this was a retrograde action, 



Figure 1.11 Dr. Ivan Vucetich. (Drawn by John Berry.) 

and he tried unsuccessfully to explain to the police authorities how superior 
fingerprint usage was to the measurement system. Fortunately in 1896, 
Argentina abandoned bertillonage and began to use vucetichissimo. (I possess 
a U.S. FBI “flyer” for someone who absconded from a state camp at Daven- 
port, Iowa, in 1929, and although the card shows his photograph and rolled 
finger impressions, it also gives numerous Bertillon measurements.) The 
Vucetich system is not in use outside South America. 

The Henry System 

The FBI, with its huge collection of fingerprint forms, uses the basic Henry 
system, amended to the FBI’s requirements. I have visited fingerprint bureaus 
in Australia, South Africa, Greece, Canada, and the U.S., and they all use the 
Henry system, which is extremely ingenious. 

On British fingerprint forms, the fingers are numbered from 1 to 5 on 
the right hand and from 6 to 10 on the left hand (see below). 



1 


2 


3 


4 


5 


RT 


RF 


RM 


RR 


RL 


6 


7 


8 


9 


10 


LT 


LF 


LM 


LR 


LL 





Whorl patterns only have values, as shown below. Even numbers on the form 
constitute the numerator, odd numbers provide the denominator. 



RT • 1 


RF ■ 2 


RM • 3 


RR • 4 


RL • 5 


16 


16 


8 


8 


4 


LT • 6 


LF • 7 


LM - 8 


LR • 9 


LL ■ 10 


4 


2 


2 


1 


1 



The finger numbers are not used in the system; totaled whorl patterns 
only apply. Therefore, if a person does not have any whorl patterns on the 
fingers, the classification would be 



0 

0 

This is a negative symbol, and therefore Sir Edward decided to always add 
“1” to both the numerator and denominator. Hence, a fingerprint classifica- 
tion without whorls would be 



1 

1 

This section has the largest number of fingerprint forms, as loops constitute 
63% of all fingerprint patterns. 

If all fingerprint patterns were whorls, the classification would be 

32 

32 

The Henry system therefore divided all fingerprint forms into 1024 bundles. 
It is quite obvious that if fingerprint forms are filed according to this system, 
the searcher chooses the bundle bearing the appropriate Henry fraction and 
merely searches this one bundle. 

There are further subclassifications, which mean that every bundle can 
be further divided for searching. Unfortunately, some fingerprint patterns 
merge their characteristics and have to be searched as alternatives, meaning 
that additional bundles have to be examined in order to positively conclude 
a search. It must also be remembered that missing or bandaged digits have 
to be further searched to cover all possibilities. Some examples of the Henry 
system classification are shown in the following table. 



w 


w 






w 


19 




w 


w 


w 




“ 24 










w 






w 




13 


w 






w 




18 



Sir Edward Henry and Sir William Herschel 

In England, an “Establishment” controversy has existed since the end of the 
nineteenth century concerning the merits of British fingerprint pioneers. 
Although the Henry system is a superb achievement, Sir Francis Galton and 
Sir William Herschel (Figure 1.12) also worked out classification systems, and 
these knights, with Sir Edward predominating, were considered to be very 
nice chaps. Herschel was an important figure in fingerprint pioneering 
because he was the first person to confirm ridge persistency, which states that 
the formation of ridge detail that develops on the hands and feet in the womb 
does not change, except as a result of serious injury to the digits or decom- 
position after death. This is the major requirement for a fingerprint system. 
I have seen the originals of Herschel’s experiments, during which he took his 
own palm impressions in 1860 and again in 1890. The ravages of time had 
caused creases to flourish across his fingers and palms, and the ridges were 
somewhat coarser, but the sequences of ridge detail remained exactly the 
same. The German anthropologist Welker also took his own palm impres- 
sions in 1856 and again in 1897, just before he died. He did not envisage any 
criminal application to his recognition that the ridge detail present on his 
fingers and palms did not change with time. 

Herschel wrote the famous “Hooghly letter” on August 15, 1877, to the 
Inspector of Jails in Bengal, India, in which he propounded the idea that 
persons committed to prison should be fingerprinted to confirm their iden- 
tities. Herschel had been experimenting with fingerprints for 20 years before 
1877 and during this time had taken thousands of fingerprints. Like Welker, 
he had never associated fingerprints with the identification of finger imprints 
found at crime scenes. 

Edward Henry must receive due credit for his practical interest in fin- 
gerprints in the latter part of the nineteenth century in India as a means of 
identifying workers to ensure that the payment of wages was not duplicated. 
However, legend and myth have arisen around Sir Edward Henry, perpetu- 
ated by writers who have produced this giant among fingerprint pioneers; 




Figure 1.12 Sir William Herschel. (Drawn by John Berry.) 

his name even now is mentioned many times daily in most fingerprint 
bureaus in the world. After all, didn’t Henry, while traveling in a train in 
India, suddenly have a flash of inspired genius whereby he quickly worked 
out the system of 1024 groups utilizing whorl patterns, as I have already 
described? In order to record this magnificent mental feat, I have read, Henry 
hastily scribbled the essential equations on his stiff and clean white shirt cuff. 
I embellish the legend every day: “I’m going to search in the ‘A’ Division 
Henry collection,” I announce. If I manage a successful “cold search” from 
finger imprints found at a crime scene, I complete a register in the office and 
under the heading Method of Identification, I write “A” Henry. I should know 
better, but habit makes a slave of thoughtlessness. It just is not true: Sir 
Edward Henry shrewdly gave his name to the classification system worked 
out by his Indian employees Khan Bahadur Azizul Haque and Rai Bahadur 
Hem Chandra Bose. Haque is alleged to have muttered to confidants that 
Henry could not even understand the system when it was patiently explained 
to him. 

There are always two versions to a controversy. Henry appeared before 
the Belper Commission in 1900. Lord Belper had been asked to chair a 
committee to decide what identification system should be used in Great 
Britain. Henry was asked point blank if the 1024 bundle system was his own 
invention, and he firmly announced that it was; in the past, writers have 
tended to support Henry’s claim. They point out that as the English official 




in charge he undoubtedly supported and encouraged his staff and should 
therefore be responsible for the innovation they suggested. In a letter dated 
May 10, 1926, Henry wrote to a correspondent concerning Haque: 

I wish to make it clear that, in my opinion, he contributed more than any 
other member of my staff and contributed in a conspicuous degree to 
bringing about the perfecting of a system of classification that has stood the 
test of time and has been accepted in most countries. 

The Belper Commission, aware that Henry’s book was due to be pub- 
lished, recommended the use of the Henry Classification System, which was 
introduced at Scotland Yard in 1901. Police forces from all over the world 
duly sent their officers to learn this new fingerprint system. 

The maintenance of a fingerprint collection serves the primary function 
of causing a file to be associated with each person whose finger impressions 
appear in the collection. When fingerprint sets are received at police head- 
quarters, the person is allocated a number; in Great Britain this is known as 
the Criminal Record Office Number (CRO No.). This number always remains 
the same for the individual, and as the individual ages and collects convic- 
tions, the file accordingly gets thicker, all convictions in the file being con- 
firmed by fingerprints taken at the time of arrest. It does happen that a person 
gives a fictitious name when fingerprinted, and if dealt with expeditiously at 
court, previous convictions will not be cited and punishment will be dealt 
out as if for a first-time offender. In the meantime, the routine is inexorably 
taking place: the fictitious name with the associated fingerprint classification 
is not found after a name search, and so the fingerprint form is then searched 
through the fingerprint collection. The true name will certainly be discov- 
ered, the alias and conviction will be added to the file, and the next time that 
person appears in court on another charge, they will discover, to their cha- 
grin, that they did not beat the system. 

The secondary use of a fingerprint collection is to provide a catchment 
area for identifying offenders who leave their fingerprints at crime scenes, 
and this has been my special province for the last 37 years. For the initial 
suggestion associating the identification of finger imprints found at crime 
scenes with finger impressions in the collections, we owe a quite considerable 
debt of gratitude to Dr. Henry Faulds. 

Dr. Henry Faulds (1843-1930) 

Henry Faulds (Figure 1.13), the son of Scottish parents, was born in Beith, 
Ayrshire, Scotland, on fune 1, 1843. He became a medical missionary for the 
Church of Scotland and spent a year in India; however, because of a clash of 
personalities with the clergy in charge, he returned to Scotland the following 



Figure 1.13 Dr. Henry Faulds. (Drawn by John Berry.) 

year. He joined the United Presbyterian Church of Scotland and married 
Isabella Wilson before sailing to Japan as a medical missionary. He arrived 
on March 5, 1874, and set up a hospital at Tsuki, in Tokyo, that was the first 
of its kind in Japan. While walking along the beach of the Bay of Yedo, he 
found ancient shards of pottery bearing the finger imprints of the potters 
(obviously not using the Getic technique of smoothness of surface). He 
became extremely interested in fingerprints. In one classical experiment, he 
removed the skin from the fingers of his patients after fingerprinting them; 
when the skin regrew on the fingertips he fingerprinted them once more, 
noting that the ridge detail was exactly the same as it was before the skin was 
removed. He recognized that fingerprint patterns were variable, but con- 
cluded that ridge detail was immutable. I believe Faulds was the person to 
identify finger imprints at crime scenes; the Japanese sought his assistance 
twice to compare scene imprints with suspects; the people he identified 
subsequently admitted to the crimes. 

I have already mentioned the amazing letter Faulds sent to Charles Dar- 
win in 1880 and Darwin’s reply mentioning Mr. F. Galton, later Sir Francis 
Galton. However, Faulds’ letter to Nature on October 28, 1880, was a most 
staggering document, and I dearly wish there was sufficient space to reprint 
the letter in full. It covered the following points: 




1. Finding finger imprints on prehistoric Japanese pottery 

2. Comparing skin furrows on humans 

3. Studying fingertips of monkeys 

4. Collecting the finger impressions of persons of various nationalities 
“which I hope may aid students of ethnology in classification” 

5. Using “an ordinary botanical lens” to examine fingerprints 

6. Describing ridge characteristics 

7. Taking finger impressions with printer’s ink, with hints on removing 
the ink afterward 

8. Discussing fingerprints of mummies 

9. Describing ancient Chinese fingerprint usage 

10. Describing the Egyptian method of thumbnail printing of criminals 

The article contained the first and most important sentence ever written 
regarding crime investigation from a fingerprint standpoint: 

When bloody finger marks or impressions on clay, glass, etc., exist, they 
may lead to the scientific identification of criminals. 

Sir William Herschel responded to Faulds’ letter by writing to Nature; 
his letter was published on November 25, 1880, and the controversy in British 
fingerprint circles dates from this time. Faulds could not possibly be privy 
to Herschel’s fingerprint experiments since he was in Japan for some of the 
time. In Fingerprint WJwrld, in conjunction with Martin Leadbetter, I pub- 
lished eight chapters of The Faulds Legacy, and regarding Herschel’s letter in 
Nature, I commented that 

... in Herschel’s own words he was working with fingerprints for twenty-three 
years prior to Faulds’ Nature letter, consequently it was surely his responsibility 
to publicly announce his researches at a time convenient to himself. 

Very belatedly, in Nature January 18, 1917, Herschel wrote: 

His [Faulds’l letter of 1880 announced ... that he had come to the conclu- 
sion, by original and patient experiment, that fingerprints were sufficiently 
personal in pattern to supply a long-wanted method of scientific identifi- 
cation, which would enable us to fix his crime upon any offender who left 
finger marks behind him, and equally well to disprove the suspected identity 
of an innocent person. (For which I gave him, and I still do so, the credit 
due for a conception so different from mine.) 

However, the battle lines had been drawn 30 years before this: the Establish- 
ment view in Scotland Yard circles was that Faulds had preempted Herschel’s 




decades of research. As recently as 1977, a senior police officer at New Scot- 
land Yard told me firmly that Faulds was a charlatan. 

Frederick Cherrill was the senior officer in charge of the New Scotland 
Yard Fingerprint Bureau for many years and was a hard-working and skilled 
fingerprint expert, visiting scenes and making identifications in major crimes 
even when of senior rank. However, in his Cherrill of the Yard (1955), he does 
not even mention Faulds in his chapter on the history of fingerprints. How- 
ever, a year previously in The Fingerprint System at New Scotland Yard (1954), 
he wrote the following on page 6: 

The value of Henry Faulds’ (1843-1930) contribution to fingerprint science 
has been much discussed, but it is beyond question that Herschel was in 
the field many years before Faulds; in fact there is incontrovertible proof 
that Herschel was experimenting with finger, palm and sole prints when 
Faulds was but 16 years old. Faulds, in his letter to Nature 28th October 
1880, entitled On the Skin Furrows of the Hand, did, however, anticipate any 
public declaration on the part of Herschel. Faulds made reference in his 
letter to the use of “nature prints” for the purpose of tracing criminals, but 
such prints were confined to visible marks made in blood, etc., and he did 
not suggest the development of latent sweat deposits from the fingers which 
now plays such an important part in modern criminal investigation. 

Faulds was annoyed when knighthoods were granted to Galton, Herschel, 
and Henry because he believed that he was the originator of the scenes-of- 
crime aspect of fingerprint identification. Indeed, Faulds was even more 
piqued when the fingerprint bureau was formed at the Yard in 1901, because 
between 1886 and 1888 he had called at the Yard and offered to organize a 
fingerprint bureau at his own expense, a suggestion which allegedly caused 
a police officer to rebuke him and make insinuations regarding his sanity. 

Faulds’ obsession, even hatred, of the Yard was revealed in 1905 when he 
allied himself with the defense at the trial of the Stratton brothers, charged 
with a double murder at Deptford, London. A thumb imprint on a cash box 
found opened at the crime scene was identified as having been made by 
Alfred Stratton. It was a good clear imprint with ample ridge detail to afford 
a positive identification, but Faulds considered it to be a “smudge” and cast 
doubts on its status. The Strattons were convicted of the murder and duly 
hanged. There was a great deal of circumstantial evidence in the case, perhaps 
strong enough to have gained a conviction without the fingerprint evidence, 
but this was the first time fingerprints had been used in a murder trial in 
England, and experts at the Yard were extremely delighted: the marvelous 
system initiated in 1901 was vindicated in this glorious triumph. Faulds was 
not amused. 




Faulds edited seven issues of a fingerprint journal Dactylography in the 
early 1920s that contained much original thought but in which he continually 
carped about “the worthy baronets”; he suffered from ill health and died in 
Wolstanton, Staffordshire, on March 19, 1930. 

The Japanese regarded Faulds with great reverence and placed a com- 
memorative stone on a tree-lined pavement in Tokyo with Japanese and 
English inscriptions. It reads: 

DR. HENRY FAULDS 

PIONEER IN FINGERPRINT IDENTIFICATION 
LIVED HERE 
FROM 1874 TO 1886. 



The Faulds family gravestone in Wolstanton was in a sorry state early in 
1987, with a dirty chipped headstone with weeds and grass covering it. Two 
American fingerprint men, James Mock, F.F.S., California, and Michael Car- 
rick, Hon. M.F.S., Salem, Oregon, paid for it to be refurbished. This was done 
and completed in April 1987. A plaque states: 

IN MEMORY OF 
DR. HENRY FAULDS 
MEDICAL MISSIONARY 
IN RECOGNITION OF HIS WORK 
AS A PIONEER IN THE SCIENCE 
OF FINGERPRINT IDENTIFICATION 
1843-1930 

THE FINGERPRINT SOCIETY 
QUAERITE ET INVENIETIS. 



This was a wonderful gesture, belatedly bequeathing to Faulds the accolade 
he deserved throughout his life but which was denied him. 

His two daughters died without having their lifelong ambition fulfilled — 
to have a bronze bust of their father placed inside Reception at New Scotland 
Yard. Strangely enough, in the corridors of the sixth floor at the Yard are a 
number of large framed aspects of fingerprints, and on one of them Faulds 
is credited with being a “Sir” — Sir Henry Faulds! Obviously, the researcher 
was confused with Sir Edward Henry. Fate indeed moves in a mysterious way. 

Sir Francis Galton (1822-1911) 

Sir Francis Gabon’s (Figure 1.14) interest in fingerprints should have been 
alerted by Dr. Henry Faulds’ letter to Charles Darwin in 1880; the letter was 
passed to Galton as promised, but he reposited it in the Anthropological 




Figure 1.14 Sir Francis Galton. (Drawn by John Berry.) 

Institute where it stayed until 1894. Galton was an authority on bertillonage, 
but it was in 1888 that he commenced his enthusiastic foray into dactylos- 
copy. Initially, he collected only thumb impressions, but in 1890 he com- 
menced to collect full sets of finger impressions. He worked out a fingerprint 
classification system and was duly called before the Asquith Committee on 
December 18, 1893; the committee was considering the Bertillon measuring 
system and pondering over a replacement. It was considered that the scope 
of Gabon’s classification system was limited when a large collection was 
envisaged, but the committee ordered that Gabon’s primary classification 
should be added to Bertillon cards. It is noteworthy that when Galton gave 
evidence before the Asquith Committee, he had 5 years of experience in the 
study of fingerprints, which accords with the present minimum standard 
requirement in order to give evidence of identity before courts of law in Great 
Britain. 

I have twice visited the Galton Laboratory in London and have had the 
extreme good fortune to examine one of the world’s most precious early 
fingerprint documents, Gabon’s Photography III, a large album containing 




much of his inspired research. For example, he pondered on the possibility 
of an intellectual aspect of fingerprint pattern distribution, and accordingly 
in one experiment he filed fingerprints into three categories: 

1. Titled persons 

2. Idiots 

3. Farm laborers from Dorset and Somerset 

He also fingerprinted a large family that included twin children. 

On one of the last pages in Photography III is a monument to early 
American fingerprint lore; a receipt reading: 

8th August 1882 

Mr. Jones, Sutler, will pay to 

Lying Bob seventy dollars. 

Gilbert Thompson. 

Written at the bottom left of the document is an arch pattern, in purple ink, 
with 75 oo/ioo written across the top. Sir Francis Galton was a great fingerprint 
pioneer as well as a man of considerable talent in many other areas. However, 
British fingerprint experts do not use the expression “Galton Ridges,” which 
is much in vogue in the U.S. 



Early Fingerprint Usage in Other Countries 
Germany 

From the first thesis by Hintz in 1747, in which spiral shapes on the skin of 
the hands and feet were discussed, numerous German researchers noted 
papillary ridges, including Schroeter, Huschke, Welker, Kollman, and Eber. 
In 1902, while studying law in Munich, Robert Heindl (1883-1958) read in 
an English magazine about the use of a fingerprint classification system and 
wrote to India for details. He stressed to German police authorities that they 
should use fingerprints for identifying people, and the first fingerprint bureau 
in Germany was set up in Dresden on April 1, 1903. However, Heindl still 
met resistance because many German police forces still thought the Bertillon 
system was superior. Nevertheless, in 1903, three other German police forces 
commenced fingerprinting: Augsburg, Hamburg, and Nuremburg. In 1912, 
a conference of all German police forces took place in Berlin, at which it was 
concluded that identification by fingerprints was superior to identification 
by the Bertillon system, and in 1911 the transition took place. 





>mp«c»c I« Cum 



Figure 1.15 Juan Steegers. (Supplied by the Cuban Ministry of Communica- 
tions. With permission.) 



Cuba 

Juan Francisco Steegers y Perera (1856-1921) was the foremost Cuban pio- 
neer in fingerprint identification; his name has been perpetuated by the issue 
of two postage stamps on April 30,1957 (Figure 1.15). Details of his life were 
presented in a philatelic commemorative booklet issued by the Cuban Min- 
istry of Communications on March 1, 1957, and the details of the pioneering 
aspect of his fingerprint achievements are presented in this translation: 

In 1904 he was elected photographer of the National Presidium, entailing 
immense work dealing with all media within his reach in order to raise the 
quality of the department; he introduced the system of utilising fingerprints 
for the identification of delinquents, thus achieving the honour of having 
introduced in Cuba the first dactyloscopic information, addressed to the 
judge of Law Instruction of the Centre. This happened on 28th November 
1907. By means of intense and constant studies Steegers created a new 
dactyloscopic-photographic medium, thus joining together dactyloscopy 
and photography and obtaining a complete result with his new discovery; 
the greatest achievement is that this same result and method are being used 
in several countries, having been given the name “Sistema Steegers.” Thanks 



to the unrelenting efforts of Steegers and his great technical ability the 
“Gabinete Nacional de Idenficacion” was created in 1911 and Steegers 
became its first director under whom the continuous technical work of 
scientific production was raised to its high level. This went on until his 
death on the 22nd March 1921. 

Canada 

Edward Foster (1863-1956) is known as the “Father of Canadian Fingerprint- 
ing.” On July 21,1910, an Order of Council was passed sanctioning the use 
of the fingerprint system in Canada. The first set of fingerprints identified 
by the Royal Canadian Mounted Police fingerprint bureau was received by 
that bureau on September 20, 1911, and was taken by Inspector Edward 
Foster. As in most parts of the world, the Canadian bureau grew daily, and 
after 9 years of operation, Foster had reportedly received more than 11,000 
sets of fingerprints that resulted in more than 1,000 identifications. By com- 
parison, in 1959, 220,000 sets had been received, giving more than 77,000 
identifications of previous convictions. 

Australia and New Zealand 

I have mentioned that Dr. Henry Faulds attempted to organize a fingerprint 
bureau at the Yard, between 1886 and 1888, at his own expense. One of the 
Scotland Yard officers he contacted was Inspector Tunbridge; although Tun- 
bridge gave the impression that he thought there was potential in a fingerprint 
system, it has been suggested that behind the scenes he was not satisfied that 
it was a workable proposition. 

In 1897, Tunbridge went to New Zealand to become Commissioner of 
Police; he retired in 1903 and returned to England. In 1907, he wrote the 
following letter to Faulds: 

I have a most distinct and pleasant recollection of our interview, and, since 
the F.P. system has been adopted as a means of identification of criminals 
with such marked success, have often wondered how it was that you have 
not been more actively connected with the carrying out of the system. When 
the Home Authorities recognised the value of the system, I was Commis- 
sioner of Police in New Zealand, and it was owing mainly to my recom- 
mendation that the system was introduced into New Zealand prisons, 
although the prison Authorities were somewhat opposed to it. Some of the 
Australian States also adopted the system, with the result that an interchange 
of prints took place, and soon manifested its value. The system is now in 
full working order in Australia, and is carried on by the police, of course, 
with the assistance of the prison Authorities. 




United States of America 



The February 1972 edition of the most excellent U.S. publication Finger Print 
and Identification Magazine mentions that a certain Thomas Taylor gave a 
lecture, some time before July 1877, stating that there was 

. . . the possibility of identifying criminals especially murderers, by compar- 
ing the marks on the hands left upon any object with impressions in wax 
taken from the hands of suspected persons. In the case of murderers, the 
marks of bloody hands would present a very favourable opportunity. This 
is a new, system of palmistry. 

The report was published in the July 1877 issue of The American Journal of 
Microscopy and Popular Science, and its implicit suggestion of identifying 
scenes of crime imprints of bloody hands predates a similar statement in 
Faulds’ Nature letter of 1880. The publication of the report in 1972 repre- 
sented a sensational revelation by author Duayne J. Dillon, Martinez, Cali- 
fornia, but it certainly does not seem to have merited the attention it mightily 
deserves. 

In 1881, Surgeon John S. Billing, U.S. Army, attended the International 
Medical Congress in London; he has been credited with making the following 
statement: 

Just as each individual is in some respects peculiar and unique, so that even 
the minute ridges and furrows at the end of his forefinger differ from that 
of all other forefingers and is sufficient to identify him . . . 

As previously stated, Galton reported the use of fingerprints by Gilbert 
Thompson in 1882 in recording the payment of wages to Lying Bob; this is 
the first instance of fingerprint usage in the U.S. 

Four years later, Taber, a San Francisco photographer, noted ridge detail 
while doodling on a blotting pad with inky thumbs; he duly photographed 
and enlarged these images. He fingerprinted his friends and associates, 
including some Chinese. At this time, large numbers of Chinese workers 
were immigrating to the U.S., and Taber wrote to the U.S. House of Rep- 
resentatives to suggest the use of thumbprints as an identification method; 
however, on the advice of experienced detectives, the idea was turned down 
in favor of facial photography, which was considered to be a sufficient 
means of identification. 

Sergeant John K. Ferrier of the Scotland Yard Fingerprint Bureau visited 
the World’s Fair Exposition in St. Louis, Missouri, in 1904 and is credited 
with giving the first lecture on fingerprints in the U.S. His message was 
somewhat messianic: he was preaching authoritatively on a new “revelation” 




and gathered around him a nucleus of “disciples” (not quite a dozen) who 
caught his every word and duly spread the “gospel according to Henry” all 
over the U.S. It is certainly no coincidence that the first U.S. police force to 
adopt fingerprinting was in St. Louis. 

The first American fingerprint lecturer was Mary K. Holland, one of 
Ferrier’s students. Gradually the use of fingerprints spread all over the U.S., 
resulting in the first conviction based on fingerprint evidence taking place 
in the state of Illinois in 1911. 

The International Association for Identification (IAI) was formed in 
1915, and, being a member, I was extremely proud to have assisted Martin 
Leadbetter in organizing the Annual Educational Conference of this august body 
in London in 1986. The IAI has been the backbone of fingerprint usage in the 
U.S. for over 74 years, and its monthly journal, Identification News, has always 
been vitally important because its contents cover all aspects of identification, 
fingerprints being merely one of the disciplines discussed in its pages. 

I have already rightly praised the Finger Print and Identification Magazine, 
which started in July 1919; it always contained important articles on funda- 
mental aspects of fingerprints, but also included little extracurricular gems. 
One of these had a tremendous influence on me! An article was written by 
PJ Putter, a fingerprint officer in the South Africa Police, in which he reported 
finding fingerprint-type ridge detail on obscure items, illustrating the article 
with photographs of cactus and mushroom peelings. I had already obtained 
a copy of Fingerprint, Palms and Soles by Cummins and Midlo, which had a 
chapter entitled “Other Patternings in Nature” (the zebra is an excellent and 
obvious example of their research into other areas where ridge detail is 
present). I became obsessed with these revelations in American publications 
of ridge detail on other items and in 1979 published the first edition of Ridge 
Detail in Nature, which consisted of 12 pages. Whereas the total number of 
examples of ridge detail was previously around one dozen, in the 1979 issue 
I quoted 44 examples. I now publish issues annually, and in the 1991 issue the 
total number of examples is 813 and requires 150 pages for their description. 
The 2001 issue had a total number of 1402 examples. 

I have also edited 64 quarterly issues of Fingerprint Whorld since July 
1975 and have always strived to follow the precepts of the Finger Print and 
Identification Magazine policy of being educational, but not inhibited by 
orthodox doctrine. For decades, fingerprint experts all over the world have 
received excellent support from the two American publications I have men- 
tioned. Finger Print and Identification Magazine ceased publication some 
years ago, but resumed in 1987, later folding. The IAI publication Identifi- 
cation News changed its size and format on January 1, 1988, and is now 
known as the Journal of Forensic Identification. Together with Fingerprint 
Whorld, these journals must continue to monitor and report on the many 




new developments and innovations that, before the turn of the century, will 
revolutionize every aspect of crime investigation. 



Developments to Date 

I vividly recall my early days visiting scenes of crimes in the mid-1950s with 
my small black case that contained a mercury-based white powder (danger- 
ous to my health), a coarse graphite-based black powder, and two stunted 
squirrel-hair brushes. If I found finger or palm marks, I had to telephone 
HQ to arrange for a photographer to visit the scene by appointment. 

Suddenly there seemed to be a burst of innovation concerning fingerprint 
evidence as part of the crime investigation. First there appeared ninhydrin, 
which was extremely efficient on paper items, especially if the stock solution 
is added to fluorisol (Freon in the U.S.), which prevents writing on the paper 
from smudging. Ninhydrin reacts with the amino acids in perspiration, pro- 
ducing red, brown, or purple imprints; this is a most successful method of 
investigating check fraud. Photography has been largely replaced by lifting 
imprints with clear tape; in Great Britain, the Camtac machine is used which, 
using the lift as a negative, produces a positive print in 90 sec with marks 
that are correct for size, color, and direction. 

During the last decade, other techniques for discovering latent imprints 
have appeared, including Super Glue, physical developer, small particle 
reagent, lasers, metal deposition, Sudan black, amido black, and radioactive 
sulfur dioxide; also, excellent powders are available with vastly improved 
fingerprint brushes. DFO is a recent improvement on ninhydrin, providing 
up to 300% more finger and palm imprints. 

Computers are now used throughout the world for the twin purposes of 
maintaining and searching files of fingerprints of offenders in “Henry” order 
and searching imprints found at crime scenes. Computer searches of crime 
scene imprints provide excellent results, but the computers are certainly not 
100% efficient. Therein lies the dichotomy. An experienced fingerprint expert 
will manually search the crime scene imprints in moderately small collections 
and will consider himself or herself to perform with 100% accuracy, stating 
categorically that the offender is not among the fingerprint forms that have 
been searched. The computer will blast through complete collections at fan- 
tastic speed, possibly scanning millions of digits, but there is no promise that 
the offender who made the imprints is not in the collection if an identification 
is not made. Computer firms who promise that their machine is totally 
efficient in this respect are knowingly prevaricating: 100% coverage without 
error will not be possible for some years. 




I find that portions of palm imprints and flexure surfaces (the inside 
lengths of the fingers) are frequently found at crime scenes, possibly in three 
out of every five crimes, and yet I am not aware of any computer develop- 
ments to search these valuable clues. Palms and flexures are extremely difficult 
to search manually 

Nevertheless, during the last 100 years, particularly since the start of its 
operational use in 1901, the fingerprint system of identification has main- 
tained its infallible status, permitting the identification of countless offenders 
but protecting millions of innocent citizens. I feel proud to have spent over 
half of my life making perhaps thousands of decisions every day with the knowl- 
edge that every one of the thousands of identifications I have made since 1955 
(including identifications at 40 murders) has been error-free based on one 
implicit factor: no person has ever been found to have ridge detail that matches 
the ridge detail on the hands and feet surfaces of any other person. 



Reference 

Napier J. Monkeys Without Tails. London: British Broadcasting Corporation, 1976. 



Addendum to the First Edition 



Regarding my paragraph suggesting lack of computer searching for palm 
imprints at crime scenes, I am delighted to report that my friend and colleague 
Martin Leadbetter B. A. (Hons), FFS, who is in charge of the Cambridgeshire 
Constabulary Fingerprint Bureau, has evolved a searching system which has 
proven highly successful in the last three years. Since 1998, computer searching 
at his bureau has revealed the magnificent total of 344 cold identifications. This 
was the world's first truly successful computer searching system. It is in use in 
the Miami-Dade Bureau, Florida, USA, and in the Garda Siochana Bureau, the 
Republic of Ireland, and they are delighted with the results. Martin can be 
contacted at the Cambridgeshire Constabulary HQ, Fingerprint Bureau, 
Hinchingbrooke Park, Huntingdon, Cambridgeshire PE 29 8NP, Great Britain. 



Update* 

In the years since this chapter was written, there has been a continuation of the 
changes that John Berry has referred to: innovations in fingerprint development, 



* By David A. Stoney, Ph.D., Director, McCrone Research Institute, Chicago, and Clinical 
Professor of Forensic Science, University of Illinois at Chicago. 




recovery, and AFIS technology. These changes are included and reviewed as 
part of this revised edition. They are important and often remarkable 
improvements in our technology. The more fundamental changes during this 
time, however, have been in our profession. We have a well-established cer- 
tification program, growing in its recognition and its adoption as a job 
requirement. We are actively debating and working to achieve standardization 
in our practices and in our educational programs. We have a professional 
journal, where there once was a newsletter, and in that journal we are seeing 
open discussions, new ideas, frequent consensus, and occasional controversy. 
These are all exceptionally good things, hallmarks of an ethical and open 
profession. 

As we progress into this next century, we also face two substantial chal- 
lenges. The first is to reexamine our premises and justify our practices before 
a new, Daubert- driven, legal ideology. The challenge is to recognize and 
appreciate this newfound scrutiny, to grow with it, and to help find our new 
place within it. We simply won’t be able to do our work the way we have and 
retain the respect that we feel entitled to. We will need to earn this respect 
by finding ways to measure the suitability of prints for comparison, to measure 
the amount of correspondence between prints, and to test the meaning of a 
given degree of correspondence. 

The other challenge is a related one. It is full integration into the forensic 
laboratory sciences. This is not a superficial, physical change in the location 
of our practice, but a conceptual and perceptual change, one that is already 
well underway. It is a movement away from dogma and toward science. It 
means letting go of some of our absolutes and opening our minds a little 
further to embrace the realities of fingerprint identification as it must 
become: less subjective, less absolute, and more correct. This transition may 
not be a comfortable one, but as we confront our fears and apply ourselves 
to the solutions, we will find that the profession will become stronger than 
ever before. 




Identification 
of Latent Prints 



2 



ROBERT D. OLSEN, SR* * 
HENRY C. LEE 



Contents 



Introduction 

Recognition and Examination 
Identification and Individualization 
Osborn Grid Method 
Seymour Trace Method 
Photographic Strip Method 
Polygon Method 
Overlay Method 
Osterburg Grid Method 
Microscopic Triangulation Method 
Conventional Method 
Experience and Skill 
Identification Protocol 
Reconstruction 
Conclusion 
References 

Introduction 



The efforts of latent print examiners are directed toward two ultimate goals: one 
is the successful developing or enhancing of a latent print, and the other is 
identification or elimination based upon the developed latent print. The pur- 
pose of this chapter is to define the principle and logic processes involved in the 
development and comparison of latent prints for the purpose of identification. 

The first mission of any latent print examiner is to recognize the potential 
areas which may contain latent prints and then to utilize one or more tech- 

* The original edition of this volume was dedicated to the merpomd lifetime work of 
Robert D. Olsen, Si; the original author of this chapterHe passed away unexpectedly 
before the first edition of the book could be published. The chapter has been updated for 
this edition by Dr Henry C. Lee. 



RECOGNITION 

i 



IDENTIFICATION 

1 

INDIVIDUALIZATION 

RECONSTRUCTION 



Scene Processing for 
Latent Prints 



Preliminary Screening 
Photography 
Lifting 

Laboratory Processing 

I 

Enhancement 

I 

Known vs. Questioned Comparison 



r 



Evaluation 

• location 

• position 

• orientation 

• condition 



■ Matching (Identification) < — i 

Non-Matching (Exclusion) — j 

1 : 

AFIS Search J 



Figure 2.1 Latent fingerprint examination. 

niques to process such an area with the objective of developing those latent 
prints and making them visible. A latent print examiner can then evaluate each 
print and make a judgment as to whether or not there are sufficient ridge 
characteristics for identification. If there are insufficient ridge characteristics 
present, then one has to determine what other methods could be applied to the 
developed print for further enhancement of the print. Once a positive decision 
is made, the second mission is to compare the developed latent print with a 
known print, with the objective of either positive identification or elimination. 

Although there have been tremendous advances in fingerprint technol- 
ogy during recent years, the basic principle and logic of these two missions 
have remained the same. In fact, the latent print examination process is the 
same as in any other type of forensic examination. The process is concerned 
with recognition, examination, identification, individualization, and evalu- 
ation (Figure 2.1). 



Recognition and Examination 



Recognition of the areas where one is most likely to find latent prints is 
probably the most important step in the examination of latent print evidence. 



Without it, no amount of further laboratory examination or automated 
fingerprint identification systems (AFIS) searches are likely to shed much 
light on the case, with regard to fingerprint evidence. If crucial latent print 
evidence is not recognized, developed, collected, and preserved, it will be 
lost, and the potential important links between a suspect and a crime may 
never be known or established. 

A latent print examiner has to possess the ability to recognize the poten- 
tial evidence that may bear latent prints. Training and experience are critical 
to the determination of what is likely to be of importance among the various 
possibilities. The recognition process involves basic principles of forensic 
examination: logical analysis of human behavior, physical examination of the 
area, surface property observation, field and laboratory processing, pattern 
enhancement, and information evaluation. 

Once the potential area which is most likely to yield fingerprint evidence 
is selected, a variety of techniques, such as physical, chemical, and instru- 
mental methods, can be used to process the surface and to develop finger- 
prints. 1 The method of choice should not be based on convenience or the 
preferences of the latent examiner. The selection of methods should rest on 
the nature of the surface, the type of matrix of the print, and the condition 
of the print. Chapter 4 covers all the major techniques currently available and 
the respective procedures for processing. The determination of whether to pro- 
cess an item of evidence for latent fingerprints at the crime scene or to package 
that item and submit it to the laboratory for further analysis is largely dependent 
on the object and surface involved (movable and immovable) and the technical 
availability at the scene (such as reagents, instruments, and personnel). 

A latent print examiner should have the ability to utilize the best meth- 
ods, or combination of techniques, for the systematic processing of a latent 
print. This also requires the examiner to possess an important additional 
form of recognition skills. The latent examiner has to have the ability to 
separate potentially important and informative ridge patterns on the devel- 
oped surface from all the background and other unrelated materials. 



Identification and Individualization 



Identification is a process common to all the sciences and, in fact, to everyday 
life. It may be regarded as a classification scheme, in which items are assigned 
to categories containing like items, and given names. Different items within 
a given category all have the same generic name. In this way, mineralogists 
will identify rocks by categorizing them and naming them. Likewise, botanists 
identify plants and chemists identify chemical compounds. A latent print 
examiner will identify fingerprints by comparing ridge characteristics. 




Objects are identified by comparing their class characteristics with those 
of known standards or previously established criteria. Comparing the class 
characteristics of the questioned evidence with those of known standards or 
control materials leads to identification. If all the measurable class charac- 
teristics are the same between the questioned sample and the known control, 
then these two samples could have come from the same source or origin. If 
there are significant differences in some of the class characteristics measure- 
ments, then the questioned sample can be absolutely excluded as coming from 
the particular source. In other words, the exclusionary value of comparison in 
the forensic field is considered absolute. Depending on the nature and type of 
the physical evidence, no further analysis can be made beyond the comparison 
step with many types of physical evidence due to inherent limitations. 

Two approaches have been used for latent print identification and indi- 
vidualization: systems engineering and human problem-solving techniques. 
They have both been modified to stress the decision-making requirements 
essential for effecting identification. This chapter is an effort to describe and 
define the identification methodology as practiced by a human latent print 
examiner and not the various algorithms employed in automated fingerprint 
identification systems (AFIS ). 2 

All training programs for latent print examiners place great emphasis on 
practical experience during the phases of instruction regarding the evaluation 
and comparison of latent prints. This emphasis is well founded and has 
considerable merit, but it has been stressed so heavily that little written 
information exists regarding the methodologies and procedures for making 
a comparison of two prints. This lack of information has resulted in a failure 
to adequately define the many tasks involved in the evaluation and identifi- 
cation processes and the subsequent failure of many persons to recognize the 
scientific nature of latent print identification. 

A description of the problem-solving techniques employed in each task 
in the evaluation and identification processes is essential for an understand- 
ing of the scientific methodology of this forensic discipline: the conceptual- 
ization of the problems encountered, the formulation of the data observed, 
and the logic that must be applied to make the decisions necessary in solving 
each problem encountered in establishing identity. 

Many experienced latent print examiners may scoff at any attempt to thor- 
oughly examine the thought processes involved in the evaluation and identifi- 
cation of latent prints. They may believe that such processes are merely common 
sense observations of physical phenomena, i.e., friction ridge characteristics. 
“Common sense, however, is based on common experience, supported and 
elaborated by the logic we apply to the explanation of that experience .” 3 Forensic 
scientists who fail to understand the scientific methodology involved in their 




work will quite often fare badly under rigorous cross-examination when 
defending their findings in a court of law. 

Individualization is unique to forensic science; it refers to the demonstration 
that a particular sample is unique, even among members of the same class. It 
may also refer to the demonstration that a questioned piece of physical evidence 
and a similar known sample have a common origin. Thus, in addition to class 
characteristics, objects and materials possess individual characteristics that can 
be used to distinguish members of the same class. The nature of these individual 
characteristics varies from one type of evidence to another, but forensic scientists 
try to take advantage of them in an effort to individualize a piece of physical 
evidence. Not all evidence can be truly individualized, but with some kinds, an 
approach to the goal of individualization is possible. We refer to those as partial 
individualization, and in some cases they are nothing more than refined iden- 
tifications, such as conventional genetic marker determination of a bloodstain, 
microscopical fiber evidence comparison, or trace elemental analysis of paint 
chips. The term identification is sometimes used to mean personal identification 
(the individualization of persons). Fingerprints, for example, are often used to 
“identify” an individual. The terminology is unfortunate, since this process is 
really individualization. Likewise, dental evidence and dental records may be 
used by a forensic odontologist in making personal individualization in situa- 
tions where dead bodies cannot otherwise be readily identified, such as mass 
disasters and cases involving fire or explosions. 

The little information that is available in the identification literature 
regarding the processes of evaluation and individualization usually covers 
only the numbers of points required for an identification or the methods of 
demonstrating an identification in legal proceedings. The methods of court- 
room presentation of fingerprint evidence may provide a clue as to the 
rationale of some examiners when making an identification in as much as 
these presentations may be viewed as models of the methodology of these 
examiners in arriving at their conclusions. In review of the available literature 
and training manuals, there are eight models currently used by latent print 
examiners for the evaluation and individualization of latent fingerprints. 

Osborn Grid Method 

The Osborn grid method (Figure 2.2) consists of photographing the latent 
and inked prints and making photographic enlargements of each. 4 A non- 
standard grid of equally sized squares is superimposed on each enlargement 
with the squares of each grid occupying identical positions on each print. Both 
prints are examined, square for square, and the points of identity in each are 
noted. If all the available points in each square are identical between the latent 
and the known print, then an identification (individualization) is declared. 





A | B 


c 


D 


E 


F 


G 


H 




1 




' 








.‘F-> 


V. v . 






2 




... ; 


.'VS/? 




T 










3 






’j/'/./s 






:yV\- *; 








4 




-4; yV 




ms 

W 




Vi;’- 


1 V. 






5 


• r / 


- 


S/ssj, 


'A*"* 






✓•/f- 






6 


d'7 


T.'r 


Sr 


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“ 























Figure 2.2 Osborn grid method. 

Seymour Trace Method 

In the Seymour trace method, the latent and inked prints are both copied 
on tracing paper. 5 The two tracings are then compared by superimposing 
one over the other and viewing them with backlighting. By tracing each point 
between the latent and the known print, a comparison is made. 

Photographic Strip Method 

The photographic strip method also involves the use of photographic enlarge- 
ments. 6 The positioning and alignment of both prints in the enlargements 
must be in as close agreement as possible. The enlargement of the inked print 
is secured to a rigid mount. The enlargement of the latent print is then cut 
in lateral strips and placed over the enlargement of the inked print. The two 
enlargements must be fastened together in perfect conjunction. The identity 
is then demonstrated by removing the strips of the latent enlargement one 
at a time, exposing the inked print below. 

Polygon Method 

The polygon method (Figure 2.3), also called the “pincushion” method, of 
demonstrating identity also requires photographic enlargements of the latent 
and inked prints; both must be made at the same scale. 7 " 9 Small pinpoint 
holes are punched in each enlargement at the corresponding ridge charac- 
teristics. The enlargements are then reversed and straight lines are drawn 
connecting the points punched. The geometric configuration of each print 
is then compared. If the polygon of pin holes between the latent and the ink 
print matches, the identity is declared. 




Latent Print 



Inked Print 



Superimposed Latent 
and Inked Polygons 



16 



Area of Latent Area of Latent 
Inside Inked Outside Inked 

Polygon. Polygon. 



Figure 2.3 Polygon method. 

Overlay Method 

The overlay method is often suggested by some examiners to demonstrate 
identity or nonidentity. 10 One approach is to place a transparent overlay over 
an enlargement of the latent print and mark the ridge characteristics with a 
suitable writing instrument. The same overlay is then placed over an enlarge- 
ment of the inked print, which must be to the same scale as the latent print, 
and the corresponding ridge characteristics are noted. 

A variation in this method is to make transparent photographic enlarge- 
ments of the latent and inked prints in two different colors, e.g., the ridge 
details of the latent may be yellow and those of the inked print may be blue. 
The latent print is then superimposed over the inked print, and matching 
ridges will appear green while nonmatching ridges will appear either yellow 
or blue. Of course, other colors have been used. 

Osterburg Grid Method 

The Osterburg grid method (Figure 2.4) is, in part, similar to the Osborn 
grid method. 11 A transparent grid is superimposed over the latent and inked 
prints, but whereas the Osborn grid has no specific measurements, the grid 
lines of the Osterburg grid are at 1-mm intervals. The Osterburg method, 
however, goes beyond simply matching characteristics in corresponding grid 
cells. Each type of characteristic is weighed according to a purported order 
of frequency, and weights are also assigned to cells without a characteristic. 
Determination of identity is made by the total value of the weighed charac- 
teristics found in a given area. No agency has officially adopted this method 
for establishing the identity of latent prints. Its application in latent print 
comparisons is entirely theoretical at this time. 




Figure 2.4 Osterburg grid method. 



Microscopic Triangulation Method 

The microscopic triangulation method is basically a combination of the grid 
and polygon methods of comparison. 12,13 A microscope is used to view the 
latent and inked prints at magnifications between lOx and 25x. A reference 
grid of hairlines in the microscopic field is used during the preliminary stage 
of the examination to scan the prints for similarities and dissimilarities. To 
establish identity, imaginary vertical and horizontal axes are drawn between 
arbitrarily selected ridge characteristics; the other characteristics are then 
plotted with respect to their relationship to the axes. This method has been 
soundly discredited and has no practical use in latent print identification. 

Conventional Method 

The conventional method is the oldest and surest method of demonstrating 
the identity of latent prints. 14,15 Identification is based on the ridge characteristics 
and their unit relationship to one another. Unit relationship, in this context, is 
not the spatial positioning of the characteristics as indicated by all the other 
demonstrative models. It is the relationship between the characteristics and all 
the other ridges in the print. The models that rely on spatial positioning do 
not take into consideration the influence of distortion in the print; it takes 
considerable experience to fully comprehend this influence. 



Experience and Skill 



Although the techniques used to process latent prints are well documented 
and most reagents are commonly available, these techniques require practice 
and training. Self-instruction in latent processing procedures and identifica- 
tion methodology without adequate guidance from a qualified instructor 
could prove disastrous. In addition, none of the methods of demonstrating 
identity attempt to define each separate task involved in the evaluation and 
comparison of latent prints. Above all, they do not explain the logical deci- 
sions that are required throughout the entire identification processes. 

Some forensic scientists consider latent print processing to be a purely 
mechanical application of a standard set of powders and chemicals onto a 
suspected surface or that latent print comparison is only a method of dem- 
onstration. Still others consider that establishing identity is merely an obser- 
vation of the spatial positioning of ridge characteristics and, therefore, that 
latent print identification is a simple procedure requiring little experience 
and that there is no need for any formal training. 

Clear and distinct prints can be demonstrated so easily that untrained 
people will fail to understand the reasons why considerable experience is 
needed to identify other latent prints. Such persons usually regard all anom- 
alies in a latent print as dissimilarities and fail to understand the natural 
effects of distortion and other adverse influences. To understand the role of 
experience in latent print identification, it is necessary to understand the 
relationship between experience and the tasks and problem-solving tech- 
niques employed in the evaluation and comparison of latent prints. A task 
may be defined as a process that is required to accomplish a measurable 
objective. A problem-solving technique is the application of certain principles 
and/or methodologies to the fulfillment of a task. 

Problem-solving, perceptual motor skills involve responses to real objects 
in the spatial world; therefore, skilled performance is usually connected with 
perceptual discrimination. There are three overlapping stages in the acquisi- 
tion of perceptual skills: cognition, fixation, and automation. Cognitive pro- 
cesses involve the conceptualization, understanding, and recognition of the 
problem encountered. The fixation stage is the longest and most difficult 
stage. During this stage the problem is fully analyzed and solutions are 
sought. The automation stage is characterized by rapid, automatic perfor- 
mance of the problem-solving skills with a minimum of errors. 

Problem-solving ability, performance, or skill in latent print identifica- 
tion may be viewed with respect to the individual’s position in the spectrum 
of expertise . 16 An individual enters the profession as a lay person and 
progresses to novice, professional, expert, and ultimately, master by virtue 
of education, research, and experience. Experience is a requirement for 




advancement throughout the spectrum. Experience is the foundation for 
superior problem-solving ability in all professions; in latent print identifica- 
tion, it is the hone for sharpening all essential skills. 

As individuals progress from one level to another along the spectrum of 
expertise, they also progress up the phylogenic scale of problem-solving 
development , 17 Experience is a vital factor in problem-solving ability because 
the greater the individual’s experience, the greater the likelihood that the 
same set of circumstances has been previously encountered and that previous 
solutions can be applied to the problem at hand. 

Superior problem-solving ability may, however, present a false impres- 
sion to lay persons and novices. They may observe only the rapidity of the 
problem-solving processes. To such persons, the evaluation and comparison 
tasks may appear to have been too easily performed and without complete 
analysis of the empirical data. Such false impressions usually give rise to the 
term “art” in describing the identification processes, a term that readily identifies 
its source as lacking an understanding of the scientific methodologies and logical 
reasoning processes required in this forensic science discipline. 

Latent print processing and visualization procedures require logical deci- 
sion making based on past knowledge. Selection of a target area to process 
is based on the principles of transfer theory and human behavior. Selection 
of a correct technique to process the target surface is based on the training 
and experience. 



Identification Protocol 



Figure 2.5 presents a problem-solving protocol and flowchart for the evalu- 
ation and comparison required in the examination of a latent print. To limit 
the description, the area for examination has been restricted to those ridge 
characteristics depicted in Figure 2.6(b). Figure 2.6(a) depicts the fingerprint 
from which the area of ridges was selected. Figure 2.6(c) is an illustration of 
how the area being examined would appear if only the spatial positions of 
the ridge characteristics were to be considered. Figure 2.6(d) is a conceptual 
enhancement of Figure 2.6(c). These last two illustrations are included to 
show the limitations of any protocols that take into consideration only the 
spatial positions of the ridge characteristics. 

Several decisions that are based mostly on experience must be made 
before comparing a latent print with an inked impression. Was the impression 
made by friction ridge skin? Is there color reversal in the image of the latent 
print? What area of friction skin made the impression? Is it possible to 
determine pattern type or ridge flow? Are there sufficient ridge characteristics 
present for comparison with an inked print? 



The initial identification of the latent print is made by comparing it with 
the inked print using 4x or 5x magnifiers. After determining the general 
pattern area of the latent print, a reference point is selected by the examiner 
to begin the search for matching characteristics in the inked print. The 
reference point may be one of the focal points of the pattern, core or delta, 
or several ridge characteristics that are near each other. After locating similar 
characteristics in the inked print, the examiner again observes the latent print 
for additional ridge characteristics that are near those previously selected and 
that match. This process is repeated until the examiner is satisfied that there 
is sufficient agreement between the two prints to form a conclusion as to 
identity. 

In addition to locating points of similarity and establishing their unit 
relationship, the examiner must also search both prints for ridge character- 
istics that may appear in one impression, but not the other: in other words, 
dissimilarities between the two prints. If the “apparent” dissimilarity can be 
explained by the examiner as the result of natural phenomena, it is not a 
dissimilarity insofar as identity is concerned. If, however, no explanation can 
be found for the dissimilarity, the examiner cannot conclude a positive iden- 
tification. This rule is often referred to in identification literature as the “one- 
dissimilarity doctrine.” 

Color reversal of latent prints is not an uncommon occurrence, and it is 
a possibility that an examiner must always consider. Color reversal occurs 
when the color of the ridges is the opposite of that expected. For example, a 
black powder is applied to a surface, but the ridges appear white against a 
black background. Color reversal may also occur when excessive pressure is 
applied, pushing the latent print residue between the ridges for final deposit 
on the receiving surface. 

If pore details are present in the print, color reversal is apparent by the 
presence of the pores in what may at first appear to be the furrows of the 
print. In some instances, the ridge characteristics may be present, but the 
ridge count between some of the characteristics may be off by one ridge. 
Generally, when there has been a color reversal of the ridges, characteristics 
such as an enclosure may appear as a short ridge. However, this is not always 
the case and it is possible to have a latent print in which the ridge events are 
the same regardless of how the color of the ridges is viewed. In instances such 
as the latter, any arguments regarding the color of the ridges would be 
superfluous and would distract from the real issue of identity. 

Distortions may be found in a fingerprint as a result of pressure applied 
to the finger or because of the curvature of the receiving surface. Failure to 
understand the effects of distortion and the techniques for resolving such 
problems has been a handicap to many inexperienced examiners. Figure 2.7 
is an example of pressure distortion in known fingerprints from the same 



Flowchart 



Protocol 




II - Examine latent print. 



D1 - Is it a friction skin impression? 



D2 - Is there image reversal? 

[If a lift, what type of lifting material was 
used?] 

D3 - Is there color reversal of the ridge details? 
[If YES, is the reversal total or partial?] 



D4 - What area of friction skin made the latent 
print? 



D5 - Determine pattern type or ridge flow. 



Figure 2.5 Flowchart. Problem-solving protocol and flowchart for the examina- 
tion of a latent print. 

finger. Note that in the core of the print on the left, there is a ridge ending, 
whereas in the print on the right, that same ridge is part of a recurving ridge. 
The examiner can readily understand and conclude that the “apparent” dis- 
similarity has been caused by pressure distortion by establishing the proper 
relationship of the ridges in the core to other ridge characteristics in the print 
and by tracing the ridges involved with a pointer. 






8 1 



D6 - Are there sufficient ridge characteristics 
present for comparison? 

Cl - Conclusion as to insufficiency of latent 
print. 

D7 - Select two or three ridge characteristics 
as reference points. 



12 - Examine inked print. 



D8 - Is the area of friction skin represented in 
the latent also in the inked print? 



D9 - Does the inked print have sufficient clarity 
for comparison? 

12-1 - Seek another card from fingerprint file for 
comparison. 



Figure 2.5 (continued) 



Reconstruction 



Reconstruction of fingerprint evidence is based on the results of crime scene 
processing of latent fingerprints, laboratory examination of physical evidence, 








DIO 



Locate reference points selected in D7. 







OP 



[If NO, return to D7 and select new 
reference points.] 



D10-1 - If unable to locate reference points after 
repeated tries, DECISION to eliminate or 
not. 



C2 - Conclusion as to non-identity. 



13 - Examine latent print. 



D1 1 - Select two or three additional points in 

close relationship to points selected in D7 
and found in DIO. 



Figure 2.5 (continued) 

comparison and identification of fingerprints, and other available data, 
records, and information to reconstruct case events. 

Reconstruction often involves the use of both inductive and deductive 
logic, statistical data, and information from the crime scene such as the 
location of the latent print, the orientation of those fingerprints, and the 
position of each print. Reconstruction can be a very complex task, linking 
many types of physical evidence, pattern information, analytic results, inves- 
tigative information, and other documentary and testimonial evidence into 





14 Examine inked print. 



D12 - Locate additional points selected in D1 1 . 

[If NO, return to D1 1 and selected new 
additional points.] 



D12-1 - Are new points selected present in inked 

print? 



D7 - If unable to locate new points after 
repeated tries, return to D7 and start 
again. 



D12-2 - If NO after repeated tries, DECISION to 
eliminate or not. 



C2 - Conclusion as to non-identity. 



Figure 2.5 (continued) 



a complete entity . 16 Latent print identification generally follows the same type 
of reasoning. The latent print examiner will identify the print by categorizing 
it based on morphological pattern recognition, physical properties of finger 
prints and palm prints, physical characteristics of ridge patterns, and spatial 
relationships of fingers on the hand. 

Latent print evaluation and comparison is primarily a visual information 
processing system. It is visual discrimination based on geometrical data and 
pattern recognition and the application of cognitive analysis. Experience 
provides a long-term data reference bank for correlation with current data 







D12 




15 - Examine latent print. 



D1 3 - Select two or three additional points in 
close relationship to points selected in 
D1 1 and found in D12. 



16 - Examine inked print. 



D14 - Locate additional points selected in D13. 

[If NO, return to D13 and select new 
additional points.] 

D14-1 - Are new points selected present in inked 

print? 



Dll - If unable to locate after repeated tries, 
return to Dll. 



Figure 2.5 (continued) 

in the latent print under examination. To understand the role of experience 
in latent print identification, it is necessary to understand the relationship 
between experience and the tasks and problem-solving techniques employed 
throughout the process of establishing identity. 

The process of identification may be separated into separate and distinct 
tasks, which, in application, an examiner would perform so automatically 
that their existence is almost undetectable. Each separate task throughout the 
identification process requires decisions that must be made regarding the 
empirical data observed and correlation of this data with previously observed 
empirical data and with experience to comprehend its significance. 





Are all points located after return to D1 1 
and repeat of procedure? 



If unable to locate after repeated tries, 
return to D7. 



If NO after repeated tries, DECISION to 
eliminate or not. 



Conclusion as to non-identity. 

Search latent and inked prints for 
unexplained dissimilarities. 

If unexplained dissimilarities present, 
DECISION to eliminate or repeat protocol. 

Conclusion as to non-identity. 

Have sufficient number of points been 
found in agreement for an identification? 



Conclusion as to positive identification. 



Figure 2.5 (continued) 



Deductive reasoning is used for making decisions throughout the iden- 
tification process, as it is essential to the methodology of all scientific disci- 
plines. In instances where the decision-making process involves retrieval of 
data from experience (long-term memory storage), the reasoning is still 
deductive if the decision is based on past observations of empirical data. 
Reliance on experience is valid because the data can be verified. 

Deductive reasoning is the process of deriving the logical consequences 
of propositions. The propositions may be based on current observations 
(empirical data from the prints being examined) and on experience (long- 
term memory storage regarding past observations). Many people are often 
unaware of the rules of inference that they employ in making deductions and 








Figure 2.6 Examination of ridge characteristics, (a) Fingerprint from which the 
area of ridges was selected; (b) area of examination was restricted to the ridge 
characteristics depicted; (c) how the area being examined would appear if only 
spatial position of ridge characteristics were considered; (d) conceptional enhance- 
ment of (c). 

derive their conclusions from premises simply by recognizing intuitively the 
connection between the familiarity of the data observed. 

Logic, in general, is the science of right thinking; it prescribes the rules 
and procedures by which conclusions can be demonstrated to be valid or 
invalid. A very brief description of deductive reasoning is necessary to com- 
prehend its role in latent print identification. In deduction, two propositions, 
which between them have a common term, are so related that from their com- 
bination a judgment, the conclusion, necessarily follows. The arrangement of 
the two propositions, termed the major and minor premises, followed by the 




It has been suggested by some lay people that latent print identification may 
not be scientific because there is no minimum standard regarding the total 
number of ridge characteristics required for a positive identification. This 
belief reflects a simplistic view that the identification process is merely the 
totaling of clearly defined ridge characteristics to obtain an arbitrary number, 
a task that may be easily performed by marginally trained technicians. 

Latent print identification is more than simply counting ridge charac- 
teristics. It involves many factors, including the skill gained only through 
experience. Latent print identification is a visual information-processing sys- 
tem employing scientific methodologies and human problem-solving tech- 
niques and requiring considerable experience for their proper employment. 
Experienced examiners, consciously or unconsciously, will consider, in addi- 
tion to the number of characteristics, the overall quality and clarity of the 
impression, the rarity of the pattern type or ridge flow, and the uniqueness 
of the ridge characteristics. 





Above all, the experienced examiner knows that the validity of the identi- 
fication can be demonstrated to the satisfaction of other qualified examiners. 
The validity of fingerprint identification is best demonstrated using the conven- 
tional method. In preparing a chart of the latent and inked prints for demon- 
stration purposes, photographic enlargements of the prints are marked by 
drawing numbered lines from selected ridge characteristics to the margins of 
the enlargements. The examiner demonstrates points of identity by using essen- 
tially the same methodology that was used in making the initial identification. 

The flowchart and protocol presented in this chapter represent one algo- 
rithm for comparing the fingerprint depicted in Figure 2.6. It must be rec- 
ognized that there can always be several algorithms for solving any problem, 
and the briefness of the algorithm presented is dictated by the limited purpose 
of this chapter: to merely acquaint the reader with the principles involved. 

Latent print examiners must be cognizant of and understand the tasks 
involved and the decisions required throughout the processes of establishing 
identity. Fingerprint identification is a science, and as such, it must have well- 
defined principles and procedures for its application. The developing fields 
of artificial intelligence and expert systems have opened up a new dimension 
in reconstruction. These systems enable the latent print examiner to model 
and make representations of laboratory analysis results, allow reasoning and 
enacting of a crime scene, and aid in making logical decisions concerning 
the case. Advances in hardware and software have added systematic problem 
solving to the forensic scientist’s repertoire. Computer technology allows 
communication between the user and the expert system — in a sense each 
is helping the other to solve a specific forensic problem. 



References 

1. Lee, H. C. and Flarris, H. A., Physical Evidence in Forensic Science, Lawyer & 
Judges, Tucson, AZ, 1999. 

2. Lee, H. C. and Gaensslen, R. E., Editors, Advances in Fingerprint Technology, 
CRC Press, Boca Raton, FL, 1991 (see also Chapter 8 of this volume). 

3. Halle, L. Out of Chaos, Houghton Mifflin, Boston, 1977, 15. 

4. Osborn, A. Questioned Documents, Lawyers Co-operative, Rochester, NY, 
1910, 479-481. 

5. Seymour, L. Finger Print Classification. Los Angeles (privately printed by 
author), 1913, 72-79. 

6. Bridges, B. Practical Fingerprinting. Funk & Wagnalls, New York, 1942, 
335-336. 

7. Brown, W., Here we go again! Finger Print Mag., 28, 5, 1947. 

8. Davis, J., Pressure distortion in latent prints. Finger Print Mag., 28, 3, 1946. 



9. Mairs, G., Novel method of print comparison. Finger Print Mag., 28, 20, 1946. 

10. Wohlfeil, P., Fingerprints in color. Tech. Photogr., 16, 28, 1984. 

11. Osterburg, J., Parthasarathy, T., Raghavan, T. et al. Development of a math- 
ematical formula for the calculation of fingerprint probabilities based on 
individual characteristics. /. Am. Statistical Assoc., 72, 772, 1977 

12. Morfopoulos, V., Anatomy of evidence. Ident. News, 20, 10, 1970. 

13. Hoover, J., Fingerprints do not lie. FBI Law Enforcement Bull, 38, 20, 1969. 

14. Cowger, J. Friction Ridge Skin: Comparison and Identification, Elsevier, New 
York, 1983, 129-189. 

15. Dondero, J. Comparing Finger Prints for Positive Identification, Faurot, New 
York, 1944. 

16. Olsen, R., Cult of the mediocre. Ident. News, 32, 3, 1982. 

17. Newell, A. and Simon, S. Human Problem Solving, Prentice-Hall, Englewood 
Cliffs, NJ, 1972. 




Composition 
of Latent Print Residue 

ROBERT S. RAMOTOWSKI 




Contents 



Introduction 
Skin Anatomy 
The Epidermis 
The Dermis 
Secretory Glands 
Eccrine Glands 

Inorganic Compounds 
Amino Acids 
Proteins 
Lipids 

Miscellaneous Constituents 
Sebaceous Glands 

Lipid Origin and Breakdown 

Chemical Composition of Sebum 

Fatty Acids 

Phospholipids 

Wax Esters 

Sterols 

Squalene 

Miscellaneous Organic Compounds 
Apocrine Glands 

Variation of Sebum Composition With Age of Donor 
Newborns 
Young Children 
Adolescents 
Post- Adolescence 

The Composition of Latent Print Residue 
United Kingdom Home Office 
Oak Ridge National Laboratory 
Pacific Northwest National Laboratory 
Savannah River Technical Center Research 
Forensic Science Service 



DNA From Latent Prints 

DNA From Blood Prints and Stains 
DNA From Developed Latent Prints 
Miscellaneous Compounds and Contaminants 
Conclusions 
References 



Introduction 



The composition of human perspiration has been studied and reported 
extensively in the medical literature. The medical community has analyzed 
sweat for many purposes, including attempts to diagnose certain diseases, 
such as cystic fibrosis, and studies of skin conditions, such as acne. Even the 
perfume and cosmetics industry has an interest in determining the precise 
chemical nature of perspiration and how it might interact with their personal 
hygiene products. However, the information ascertained in these studies does 
not begin to address the issue that is most critical for forensic scientists. 
Knowing the precise contents of the various skin glands does not accurately 
represent the nature of what is actually secreted onto substrates from the 
fingers and palms. In operational scenarios, numerous contaminants are present 
in the fingerprint deposit, including material from other glands, cosmetics, 
perfumes, and food residues. In addition, the secreted material is almost imme- 
diately altered by oxidative and bacterial degradation mechanisms. These factors 
are particularly important since crime scene technicians seldom encounter latent 
print deposits immediately after they are deposited by a perpetrator. However, 
there is little information available that describes how a latent print deposit 
changes with time. Thus, a more thorough understanding of these transforma- 
tions would allow forensic scientists to develop specific reagents for visualizing 
compounds known to be stable for long periods of time. 



Skin Anatomy 

Skin serves several functions, including regulation of body temperature, 
water retention, protection, sensation, excretion, immunity, blood reservoir, 
and synthesis of vitamin D (except where noted, the information in this 
section was obtained from Odland 1 ). The skin of an average adult exceeds 

2 m 2 in area; yet, in most places it is no more than 2 mm thick. While the 
average thickness of epidermal skin varies little over most of the body, the 
thickness on the palms and soles can be as much as 0.4 to 0.6 mm. The skin 
is usually divided into two distinct layers. The outer layer is a stratified 



epithelium called the epidermis, which has an average thickness of 75 to 
150 pm. The underlying layer of skin is called the dermis, a dense fibroelastic 
connective tissue that constitutes the primary mass of the skin. This portion 
of the skin contains most of the specialized excretory and secretory glands 
that produce sweat. Although the dermis constitutes between 90 to 95% of 
the mass of human skin, the epidermis accounts for the major proportion 
of the biochemical transformations that occur in the skin (although struc- 
tures that extend into the dermis, such as the various sweat glands and hair 
follicles, are also metabolically important). 

The Epidermis 

The epidermis (Figure 3.1) consists of several cell layers. 2 The innermost is 
known as the stratum germinativum (basal cell layer). It consists of one layer 
of columnar epithelial cells, which upon division push into the stratum 
spinosum. The stratum spinosum (prickle cell layer) consists of several layers 
that are held together by intercellular fibrils. The combined stratum spino- 
sum and stratum germinativum are often referred to as the Malpighian layer 
(named in honor of Marcello Malpighi, a 17th century Italian professor and 
fingerprint science pioneer who first used high magnification to detail the 
fine structure of ridges and pores). 

As these cells approach the skin surface, they begin to grow larger and 
form the next layer, the stratum granulosum (granular layer). Keratohyalin 
granules (the precursor of keratin, a fibrous, insoluble protein found in skin) 
are formed in this layer, which is approximately two to four cells thick. The 
nuclei are then either broken up or dissolved, resulting in the death of the 
epidermal cell and an increase in the number of cytoplasmic granules. The 
penultimate layer, the stratum lucidum (clear layer), is ill-defined and con- 
sists primarily of eleidin, which is presumed to be a transformation product 
of the keratohyalin present in the stratum granulosum. In the outermost 
layer, the stratum corneum (cornified layer), the eleidin is converted to ker- 
atin, which is the ultimate fate of the original epidermal cell. Keratin, which 
is continually sloughed off, must continuously be replaced by cells beneath 
it. It has been estimated that a typical individual will shed approximately 0.5 
to 1 g of dead skin cells per day. 2 The total cell cycle in the epidermis is 
estimated to take approximately 28 days. Figure 3.2 is a stained skin section 
showing all of the layers of the epidermis. 

The Dermis 

The dermis is a moderately dense fibroelastic connective tissue composed of 
collagen (a fibrous protein composed of primarily glycine, alanine, proline, 
and hydroxyproline), elastin fibers (a fibrous protein containing primarily 




Basal Lamina 



Figure 3.1 A schematic diagram showing the layers of the epidermis. (From The 
Structure and Function of Skin, 3rd Edition, Montagna, W. and Parakkal, P.F., 
Eds., Academic Press, 1974. With permission.) 

glycine, alanine, valine, and lysine), and an interfibrillar gel of glycosamin- 
proteoglycans, salts, and water. This layer contains up to five million secretory 
glands, including eccrine, apocrine, and sebaceous glands . 2 Collagen fibers 
form an irregular meshwork that is roughly parallel to the epidermal surface 
and provides skin tensile strength and resistance to mechanical stress. Elastin 
gives skin its elasticity and its ability to resume its natural shape after defor- 
mation. Fibrous mats of elastin are intermeshed with collagen to give skin 
its tension. This tension is greatest over body areas where the skin is thin and 
elastin is abundant (e.g., the scalp and face). Fibroblasts, which form elastin 
and collagen, and histiocytes, which form interferon for protection against 





Figure 3.2 A stained section of the epidermis from the palm showing all of the 
layers. Section A is the stratum corneum, section B is the stratum lucidum, 
section C is the stratum granulosum, and section D is the stratum malpighii. 
The structure evident in the stratum corneum is the duct of an eccrine sweat 
gland. (From The Structure and Function of Skin, 3rd Edition , Montagna, W. and 
Parakkal, P.F., Eds., Academic Press, 1974. With permission.) 

viral infections, are present in this layer. A system of blood, lymphatic, and 
nerve vessels is also present. 

The dermis is divided into two anatomical regions, the pars papillaris 
and the pars reticularis. The papillary dermis is the outermost portion of the 
dermal layer and contains smaller and more loosely distributed elastin and 
collagen fibrils than does the reticular dermis. The papillae are supplied by 
numerous capillaries, which ultimately supply nourishment to the epidermis 
via diffusion. The second region, the reticular dermis, lies beneath the pap- 
illary dermis and comprises the bulk of this layer. It is characterized by dense 
collagenous and elastic connective tissue. These collagen bundles are 
arranged predominately in interwoven strands that are parallel to the skin 
surface, although some tangentially oriented bundles are present. 






Figure 3.3 A schematic diagram of the three major secretory glands in relation 
to other cutaneous appendages. (From The Structure and Function of Skin, 3rd 
Edition, Montagna, W. and Parakkal, P.F., Eds., Academic Press, 1974. With 
permission.) 



Secretory Glands 

The three major glands (eccrine, apocrine, and sebaceous) responsible for 
the secretion of “sweat” are shown in Figure 3.3. The eccrine glands are 
usually found throughout the body, but the highest densities are found in 
the palms and soles. The sebaceous glands are typically localized to regions 
containing hair follicles, as well as the face and scalp. The apocrine glands 



are found primarily in the axillary regions (e.g., armpits and genital areas). 
However, in most instances, only the eccrine and sebaceous glands contribute 
significantly to the latent print deposit. Although the composition of sweat 
is approximately 99% water, 3 studies have shown that a considerable variety 
of chemical compounds are present. A recent study found approximately 346 
compounds (303 of which were positively identified) present in surface skin 
residues. 4,5 

Eccrine Glands 

There are between two and four million eccrine sweat glands distributed 
throughout the human body surface (except where noted, the following 
information was obtained from Quinton 6 ). Each gland has been calculated 
to have an estimated weight of 30 to 40 pg, for an aggregate weight of about 
100 g. In normal individuals, these glands are capable of secreting as much 
as 2 to 4 L of fluid per hour. The evaporation of this quantity of sweat requires 
approximately 18 kcal/min, which affords humans an ability to dissipate heat 
faster than any other animal. Sweat glands are most abundant on the soles 
of the feet (620/cm 2 ) and least abundant on the back (64/ cm 2 ). 7 Gland for- 
mation begins around the third fetal month on the palms and soles and at 
about 5 months for the rest of the body. Typically, the glands have fully 
matured by the eighth fetal month. The eccrine gland is essentially a tubular 
shaped structure with a duct portion that coils in helical fashion down deep 
into the dermis layer. The function of the distal half of the sweat gland tubule 
is to reabsorb sodium, chloride, bicarbonate, glucose, and several other small 
solutes. Under normal conditions, this allows water to be evaporated from 
the skin surface without the loss of essential solutes. 

Inorganic Compounds 

Although eccrine sweat is usually in excess of 98% water, it also contains 
numerous organic and inorganic constituents. The presence of these solutes 
on the skin surface causes a reduction in sweat vapor pressure. These effects 
have been modeled and quantified. 8 Excess secretion of certain chloride salts 
has been reported to be a cause for increased rates of corrosion of metal 
surfaces by particular individuals. 9 This effect was particularly pronounced 
in patients suffering from hyperhidrosis, a condition which causes excess 
sweat production. The rate of eccrine sweating has been shown to depend 
on the amount of water ingested, but does not appear to exert an independent 
effect on the relationship of sweat composition to sweat rate. 10 Sweat has 
been reported to contain 0.5 to 8 m M total ammonia, 11 which is 20 to 50 
times higher than plasma levels. In addition, trace amounts of the following 
inorganic substances have also been detected in sweat: magnesium, iodide 




(5 to 12 pg/L), bromide (0.2 to 0.5 mg/L), fluoride (0.2 to 1.18 mg/L), phos- 
phate (10 to 17 mg/L), sulfate (7 to 190 mg/L), iron (1 to 70 mg/L), 12 zinc, 
copper, cobalt, lead, manganese, molybdenum, sulfur, tin, and mercury. 1315 

Interestingly, the eccrine gland is one of the target organs for cystic 
fibrosis. Historically, this condition has been diagnosed on the basis of ele- 
vated sodium chloride concentration in sweat. In general, the sweat sodium 
ion concentration appears to be isotonic to that of human plasma, although 
significant variations can be obtained depending on the method of collection 
(e.g., thermal vs. pharmacologically induced sweat). 16 One study found that 
the sodium concentration varied over a rather large range, from 34 to 266 
mEq/L. Others reported the average concentration at 140 ±1.8 mEq/L 7 and 
60 mEq/L. 17 The latter source reported that the chloride concentration is 
generally lower than that of sodium, averaging around 46 mEq/L, and that 
the potassium level ranged from 5 to 59 mEq/L. In general, chloride levels 
are isotonic with those in plasma. 18 Other studies have determined the potas- 
sium levels to be between 4.9 to 8.3 mEq/L 16 and 8.8 mEq/L. 19 The amount 
of calcium in sweat was found to be about 3.4 mEq/L and the amount of 
magnesium was 1.2 mEq/L. 

The HCO. -CO, buffer system appears to play a critical role in maintain- 
ing sweat pH. The pH of sweat isolated from human secretory coils (in the 
dermis) is approximately 7.2, while the pH of sweat secreted from the gland 
can vary from as low as 5.0 (at a low sweat rate) up to 6.5 to 7.0 (at a high 
sweat rate). This indicates that the duct itself acidifies the sweat, presumably 
by reabsorbing bicarbonate and/or secreting H + in exchange for a Na + ion. 20 
At low sweat rates, this mechanism can conserve bicarbonate (and other 
solutes) efficiently and thus maintain a slightly acidic sweat pH. At higher 
sweat rates, the mechanism is overwhelmed and cannot reabsorb solutes 
effectively. This results in secreted sweat containing higher amounts of bicar- 
bonate and thus it has a higher pH. The typical bicarbonate concentration 
has been reported to be between 15 to 20 m M. 

Amino Acids 

Of critical importance to latent print visualization with ninhydrin is the 
concentration of amino acids and proteins. The total amount of amino acids 
present in a print has been reported to be between 0.3 to 2.59 mg/L. 14 The 
first amino acid found in eccrine sweat was serine, isolated as (3-naphtha- 
linesulfoserine by using a microbiological method, and was reported by 
Embden and Tachau in 1910. A study of samples of pharmacologically 
induced sweat (using pilocarpine hydrochloride) collected after a hygienic 
bath yielded 22 amino acids. 21 Amino acid amounts in sweat have been 
reported to be several times higher than corresponding values in plasma. 22 
One study found the most abundant amino acids to be serine and alanine, 




Table 3.1 A Summary of the Relative Abundance 
(Serine Ratio) of Amino Acids in Fingerprint Deposits 





Hamilton 28 


Hadorn et al. 27 


Oro and Skewes 29 


Serine 


100 


100 


100 


Glycine 


67 


54 


59 


Ornithine 


32 


45 


45 


(Ornithine, lysine) 


42 


47 


45 


Alanine 


27 


35 


28 


Aspartic acid 


22 


11 


22 


Threonine 


17 


9 


18 


Histidine 


17 


13 


14 


Valine 


12 


10 


9 


Leucine 


10 


7 


10 


Isoleucine 


8 


6 


8 


Glutamic acid 


8 


12 


5 


Lysine 


10 


5 


— 


Phenylalanine 


7 


5 


5 


Tyrosine 


6 


3 


5 



15.44 and 14.63 mg%, respectively. Another study of both active and inactive 
participants found that in both cases, serine, glycine, and alanine were the 
most abundant amino acids. 23 A similar trend was also reported by several 
others. 24 ' 26 

Quantitatively, amino acid concentrations can vary as much as 2 to 20 
times depending on collection methods (e.g., thermally induced sweat vs. 
exercise-induced sweat) and by sample location on the body. A study com- 
paring sweat samples obtained from the back and hands of subjects found 
some significant differences. 27 The samples from the backs of subjects showed 
higher amounts of amino acids involved in the urea cycle. These and other 
differences appeared to be independent of plasma and urine amino acid 
levels, suggesting that amino acids do not appear in sweat as a result of 
filtration from the blood plasma. Table 3.1 summarizes the relative amino 
acid abundance values from several different studies. One study reported a 
series of ninhydrin positive substances, in addition to amino acids, in human 
eccrine sweat. 30 Some of these substances include o-phosphoserine, methion- 
ine sulfoxide, a-amino-isobutyric acid, glucosamine, a-amino-n-valeric 
acid, cystathionine, (3-amino-isobutyric acid, ethanolamine, y-amino- 
butyric acid, and carnosine. 

Proteins 

The total protein content in sweat has been determined to range between 15 
to 25mg/dL. One study using two-dimensional electrophoresis and ultra- 
sensitive silver staining found over 400 polypeptide components. 31 Some 
specific examples determined by sodium dodecyl sulfate polyacrylamide gel 



electrophoresis (SDS-PAGE) include albumin, Zn-cx 2 -glycoprotein, 
lysozyme, and the a r acid glycoprotein orosomucoid. 32 An agarose gel iso- 
tachophoresis analysis of thermally induced sweat detected transferrin, fast- 
migrating y-globulins, a- and (3-lipoproteins, and several glycoproteins. 33 It 
has been determined by size fractionation HPLC that the bulk of the peptides 
in sweat are in the low end of the molecular weight range. Secretion of higher 
molecular weight proteins (i.e., in excess of 10,000 Da) has been reported to 
increase as the rate of sweating increases. 

Lipids 

The lipid content of secretions from the eccrine gland has also been investi- 
gated. 34 Contamination of samples by lipids of sebaceous and epidermal 
origin is a major consideration in these analyses. In this particular study, thin 
layer chromatography was used to separate the lipid fraction collected from 
both “clean” and “scraped” sweat samples. Results indicated that the 
“scraped” samples contained a significant amount of lipids that were consis- 
tent with those found in the stratum corneum. In contrast, the “clean” sam- 
ples collected using the method described by Boysen et al. 35 contained only 
one significant lipid band, which corresponded to the cholesterol/ fatty acid 
standard. In the samples collected, fatty acid concentrations ranged from less 
than 0.01 to 0.1 pg/mL and sterol concentrations ranged from less than 0.01 
to 0.12 pg/mL. These results would indicate that “scraped” samples were 
contaminated by lipids from the epidermis, while “clean” samples gave a more 
realistic characterization of eccrine lipids. 

Miscellaneous Constituents 

Lactate and urea have been reported at significant levels in perspiration. The 
amounts of these compounds can vary from 30 to 40 m M at low sweat rates 
to as low as 10 to 15 m M at higher rates. 13 Other miscellaneous components 
of eccrine sweat include creatine, creatinine, 36 glucose (0.2 to 0.5 mg/dL), 
pyruvate (0.2 to 1.6 m M), cAMP, phenobarbitone, and immunoglobulins. 37 
Numerous enzymes have also been detected in dissected sweat glands, includ- 
ing alkaline phosphatase, acid phosphatase, Na/K ATPase, phosphatidic acid 
phosphatase, monoamine oxidase, acetyl cholinesterase, and lactic, malic, 
glucose-6-phosphate, isocitric, and succinic dehydrogenases. 

Drugs have also been found in eccrine sweat. 38 Sulfonamides, antipyrine, 
and aminopyrine were found to exhibit sweat concentrations that were 
directly proportional to plasma levels. Simple diffusion, aided by the relatively 
low ionization of the drugs studied within the physiological pH range, was 
assumed to be the mechanism by which these drugs entered the sweat glands. 
Another study found that L-dimethylamphetamine as well as its metabolite 
L-methamphetamine were found to be excreted in sweat. 39 After taking 25 mg 




Table 3.2 A Summary of the Composition of Eccrine Sweat 



Inorganic (major) 




Inorganic (trace) 




Sodium 


34-266 mEq/L 


Magnesium 




Potassium 


4. 9-8. 8 mEq/L 


Zinc 




Calcium 


3.4 mEq/L 


Copper 




Iron 


1-70 mg/L 


Cobalt 




Chloride 


0.52-7 mg/mL 


Lead 




Fluoride 


0.2-1.18 mg/L 


Manganese 




Bromide 


0. 2-0.5 mg/L 


Molybdenum 




Iodide 


5-12 pg/L 


Tin 




Bicarbonate 


15-20 mM 


Mercury 




Phosphate 


10-17 mg/L 






Sulfate 


7-190 mg/L 






Ammonia 


0.5-8 mM 






Organic (general) 




Organic (lipids) 




Amino acids 


0.3-2.59 mg/L 


Fatty acids 


0.01-0.1 pg/mL 


Proteins 


15-25 mg/dL 


Sterols 


0.01-0.12 pg/mL 


Glucose 


0. 2-0.5 mg/dL 






Lactate 


30-40 mM 






Urea 


10-15 mM 






Pyruvate 


0. 2-1.6 mM 






Creatine 








Creatinine 








Glycogen 








Uric acid 








Vitamins 








Miscellaneous 








Enzymes 








Immunoglobulins 









Note: Some compounds and species were only listed as present in sweat in the literature. No 
concentrations were specified for these components. 



of the L-dimethylamphetamine, the maximum concentration in sweat was 
found to be approximately 2 to 4 pg/mL, within a few hours after ingestion. 
Unlike the urine concentration, L-dimethylamphetamine levels in sweat were 
found to be independent of pH. Ethanol has also been detected. Several 
relatively rapid, noninvasive methods have been proposed to examine the 
ethanol (as well as other volatile organics) present in perspiration. 40 The 
composition of eccrine sweat is summarized in Table 3.2. 

Sebaceous Glands 

The second major class of secretory glands, sebaceous glands, are located 
throughout the body, except for the palms and dorsum of the feet (except 
where noted, the information in this section was obtained from Strauss 



Table 3.3 Anatomical Variation in the Amount and Composition of Human 
Sebum Collected After 12 hr of Accumulation (in Weight Percent) 



Site 


Total lipid 
(pg/cm 2 ) 


CH 


CE 


TG 


DG 


FA 


WE 


SQ TG+DG+FA 


Forehead 


288 


1.1 


2.7 


29.6 


3.5 


27.2 


25.9 


10.1 


60.3 


Cheek 


144 


1.1 


3.4 


39.4 


2.7 


15.4 


26.9 


11.2 


57.5 


Chest 


122 


1.3 


2.6 


29.7 


5.4 


24.9 


25.7 


10.3 


60.0 


Back 


84 


2.2 


2.0 


35.9 


4.5 


17.4 


27.4 


10.6 


57.8 


Arm 


76 


4.8 


4.3 


34.3 


2.4 


18.4 


27.7 


8.1 


55.1 


Side 


57 


4.3 


4.5 


47.1 


1.9 


7.6 


24.9 


9.6 


56.6 


Leg 


57 


6.3 


6.0 


44.6 


1.5 


10.2 


23.1 


8.1 


56.3 



Note: CH = cholesterol; CE = cholesterol esters; TG = triglycerides; DG = diglycerides; FA = free fatty 
acids; WE = wax esters; SQ = squalene; and TG + DG + FA = total glycerides plus free fatty acids. 



Source: Greene, R. S., Downing, D. T., Pochi, P. E., and Strauss, J. S., Anatomical variation in the 
amount and composition of human skin surface lipid. J. Invest. Dermatol., 54(3), 246, 1970. 
With permission. 



et al. 41 ). Gland density is greatest around the face and scalp, where as many 
as 400 to 800 glands per cubic centimeter may be found. The sebaceous 
glands are generally associated with hair follicles and open inside the hair 
shaft canals. Unlike eccrine secretions, which empty directly onto the skin 
surface, the sebum produced by sebaceous glands first travels into the folli- 
cular canal and then onto the skin surface. The lipid is produced by a holo- 
crine mechanism, whereby lipid-laden cells disintegrate and empty their 
contents through the sebaceous duct onto the skin surface. 42 These glands 
develop during fetal life between weeks 13 and 15 and have achieved a nearly 
full size by the time of birth. 43 The glands are fully developed and functioning 
before birth, probably due to stimulation by maternal hormones. At birth, 
with the termination of the source of these hormones, the glands soon 
become mostly inactive. Table 3.3 summarizes sebum production and com- 
position for various anatomical regions. 44 

Sebaceous gland activity appears to be controlled by a somewhat complex 
process. It appears that mid-brain dopamine stimulates the anterior and 
intermediate lobes of the pituitary gland to release various hormones via 
certain glands (e.g., thyroid, adrenals, and gonads). 45 In turn, these glands 
secrete additional hormones that stimulate sebum production. Several 
androgens have been found to stimulate sebum production. 46 Testosterone 
is an especially potent stimulator of sebum production in humans. It has 
been reported that sebum production levels in castrated males are consider- 
ably lower than in intact men. 47 The administration of testosterone to cas- 
trated males has been reported to result in a significant increase in sebaceous 
gland activity. 48 However, administration of testosterone to the normal adult 
male does not lead to an increase in sebum production. This would indicate 



Table 3.4 The Approximate Composition of Sebum 
and Surface Epidermal Lipids 



Constituent 


Sebum 

(wt%) 


Surface epidermal lipid 
(wt%) 


Glyceride/free fatty acids 


57.5 


65 


Wax esters 


26.0 


— 


Squalene 


12.0 


— 


Cholesterol esters 


3.0 


15 


Cholesterol 


1.5 


20 



Source: Downing, D. T. and Strauss, J. S., Synthesis and composition 
of surface lipids of human skin, J. Invest. Dermatol., 62, 231, 
1974. With permission. 



that maximum stimulation of the sebaceous glands is accomplished by 
endogenous testosterone. Other studies have found slight increases in skin sur- 
face lipids after administering testosterone. 49 Testosterone given to children also 
produced a significant increase in sebum production. 50 Metabolism and elim- 
ination of these compounds in human skin samples has been reported. 51 It 
appears that excretion of C 19 - and C 18 -steroids through the skin may exceed 
their urinary elimination. 

Lipid Origin and Breakdown 

Radioactive labeling studies have illuminated the formation and origin of 
lipids. 52 Autoradiograms from one study showed that radioactivity (from 
incubating samples of subcutaneous fat from scalp biopsies with [ 14 C] ace- 
tate) found in total lipid extracts was confined to squalene, wax esters, tri- 
glycerides, and phospholipids. It is significant to note that cholesterol, 
cholesterol esters, and free fatty acids did not contain any significant amount 
of radioactivity. That would imply that these compounds are of epidermal 
origin rather than being produced in the sebaceous gland. The differences 
in lipid classes between lipids of sebaceous and epidermal origin are listed 
in Table 3.4. Another study proposed that sebaceous lipids are derived from 
two different sources, the body’s circulation (exogenous lipid) and from de 
novo synthesis (endogenous lipids). 53 They assumed that the composition of 
both of these sources remained constant, but that their relative contribution 
to sebum was variable. Examples of possible exogenous lipids would include 
linoleate (an essential fatty acid), cholesterol, cholesterol esters, and triglyc- 
erides. However, the fact that circulating cholesterol esters and triglycerides 
have different fatty acid compositions than their sebaceous counterparts 
makes it unlikely that they are incorporated directly into sebum. Examples 
of endogenous lipids that are not available from blood include A6 fatty acids, 
squalene, and wax esters. 



Various oxidative and bacteriological changes occur after sebum is 
excreted. Lipolysis by enzymes derived from the epidermis or bacteria present 
in skin surface debris from human skin has a tendency to break down tri- 
glycerides and methyl esters. 54 That particular study reported that, in ether, 
triolein and tristearin were converted primarily to free fatty acids and 1,2-di- 
glycerides and only trace amounts of 1,3 -diglycerides and monoglycerides. 
This evidence leads to the conclusion that the majority of free fatty acids 
present in sweat originate from the hydrolysis of sebum triglycerides. Evi- 
dence of varying degrees of bacterial lipolysis has been offered for Coryne- 
bacterium acnes, 55 ' 56 staphylococci, 57 Pityrosporum ovale , 58 Pityrosporum 
acnes, Pityrosporum granulosum, 59 Micrococcaceae, and propionibacteria. 60 
Several studies have shown that treatment of skin with antibiotic compounds 
(e.g., clindamycin) reduced bacterial populations and led to a concurrent 
decrease in free fatty acids. 61-63 However, one study found that treatment with 
neomycin failed to affect the C. acnes population. 64 It is likely that certain 
bacteria, such as C. acnes, are present within the hair follicles and would be 
inaccessible to topical antibiotics. 

Chemical Composition of Sebum 

There is a considerable variety of organic compounds present in sebum. 
Several factors can influence a particular individual’s sebum profile, including 
diet and genetics. It is possible that each person may have a unique scent 
signature, as demonstrated by the ability of certain breeds of dogs to track 
humans over wide areas. In addition, in animals, certain lipids may function 
as a means of communication. One study determined that in certain species, 
short-chained aliphatic acids were found to act as pheromones. 65 These com- 
pounds also allow animals to recognize members of their own social group. 
It is possible that a similar situation was once present in humans; however, 
modern hygiene practices may have diminished our ability to recognize the 
signals. In fact, in humans, sweat has to be broken down bacterially before 
it acquires a detectable, characteristic odor. A summary of sebum composi- 
tion by lipid class is presented in Table 3.5. 

Fatty Acids 

Hydrolysis of human sebum results in the formation of a mixture of fatty 
acids. The amount of free fatty acids in sebum shows considerable variation, 
but averages between 15 to 25%. They are derived primarily from the hydrol- 
ysis of triglycerides and wax esters. It has been proposed that as the amount 
of liberated free fatty acids increases to a certain concentration, the pH drops 
sufficiently to inhibit bacterial lipases responsible for their production. 64 It 
has been reported that patients with acne have elevated levels of free fatty 
acids, typically greater than 30%. 71 It has also been observed that free fatty 



Table 3.5 Summary of Sebum Composition 





Downing 
et al. 66 


Lewis 

and 

Hayward 67 


Haahti 68 


Nicolaides 

and 

Foster 69 


Felger 70 


Nordstrom 
et al. 71 


Goode 

and 

Morris 3 


Darke 

and 

Wilson 72 


Glycerides 


43.2 


46.4 


42.6 


31.7 


35.4 b 


16.1 


33 


30.2 C 


Fatty acids 


16.4 


16.0 


16.2 


29.6 


27.2 b 


33.0 


30 


22.0 


Wax esters 


25.0 


21.5 


24. 2 a 


21.8 


22.6 


25.3 


22 


29.3 d 


Cholesterol 


2.1 


2.9 


— 


3.3 


2.5 


2.0 


2 


— 


esters 

Cholesterol 


1.4 


1.8 


1.4 


2.4 


0.7 


3.8 


2 


1.1 


Squalene 


12.0 


11.4 


15.6 


12.8 


11.6 


19.9 


10 


17.4 



a This value is for both wax and cholesterol esters. 

b The differences between these and other values listed are more than likely caused by individual differences in the degree of 
lipolysis of triglycerides by bacterial lipases. 
c This value includes cholesterol esters. 
d This value includes a minor contribution from diglycerides. 




acid content can change with time in the same individual. One study found 
that certain fatty acids from the same donor taken once a week for 7 weeks 
showed significant variation in concentration with time. 73 The study also 
reported significant differences between male and female fatty acid compo- 
sition. In addition, minor differences were observed between fatty acids 
isolated from wax esters and cholesterol esters. However, it is difficult to draw 
conclusions from this data since only two subjects were involved in the study. 

Approximately 50% of the fatty acids in sweat are saturated, with straight 
chain C 16 and C 14 being the dominant acids. 74 Monoenes typically constitute 
48% of fatty acids, with straight chain C 16 and C 18 being the most prominent. 
The structures of unsaturated fatty acids have been reported to vary with age 
and sex. 75 The amounts of A9-type unsaturated fatty acids (in triglycerides, 
wax esters, and sterol esters) were always higher in females than in males. 
The amount of A9-type unsaturated fatty acids reaches a maximal value 
during the prepubertal years, decreases to a minimum from adolescence to 
middle age, and then begins to increase again with advancing age. In nature, 
A9-type monounsaturated compounds are the most common and A6-type 
are relatively rare. Interestingly, the presence of A6-type fatty acids in humans 
appears to be virtually unique among species studied. 76 Also, A6-type unsat- 
urated fatty acids are almost exclusively derived from sebaceous glands, 
whereas A9-type acids appear to be primarily of epidermal origin. Dienoic 
fatty acids comprise about 2 to 3% of samples, with major isomers being 
18:A5,8 and 18:A9,12. 77 Increased levels of the 18:A5,8 diene have been 
reported in acne patients. 78 

Several branched chain fatty acids have been detected in humans. The 
largest variation occurred with iso-even fatty acids. One study found signif- 
icant variations (10- to 20-fold) in the amounts of iso-branched acids having 
an even number of carbons. 74 Odd-carbon iso- and anteiso -branched acids 
showed only a threefold variation among individuals tested. Another study 
examined the possibility that genetics controls the proportions of iso-even 
fatty acids by analyzing the sebaceous wax esters of twins. 79 While the general 
population has large variations in the proportions of iso-even fatty acids, 
intrapair differences in 13 pairs of identical twins were found to be very small. 
It has been suggested that slight differences in the overall composition of the 
sebaceous fatty acid mixture could lead to unique, individual odors in 
humans. 76 Another study found that certain short chain fatty acids, such as 
iso-valeric acid (iso C 5 ), are responsible for “offensive” human odors. 80 

Phospholipids 

Phospholipids, which are present in the membranes of sebaceous cells, are 
typically not found in surface sebum. Although epidermal cells have phos- 
pholipids, the stratum corneum is virtually devoid of them. This is most 




likely due to their degradation in the granular layer, a process that allows for 
re-absorption of essential nutrients, such as phosphorus and choline. In the 
epidermis, fatty acids liberated by this degradation process remain in the 
keratinizing cells and become partly esterified with cholesterol. A similar 
mechanism has been proposed for fatty acids liberated in the sebaceous 
glands. However, the lack of cholesterol diminishes the probability of fatty 
acid esterification. Likewise, a lack of glycerol limits the formation of tri- 
glycerides. The study concluded that these fatty acids are most likely reduced 
to fatty alcohols and then esterified to form wax esters. 

Wax Esters 

On average, wax esters comprise approximately 20 to 25% of adult skin 
surface lipids. Wax esters are compounds that contain a fatty acid esterified 
with a fatty alcohol. Free fatty alcohols have not been found in human skin 
surface lipids, possibly due to the inability of bacterial or epidermal lipases 
to hydrolyze wax esters. 80 A study of the fatty alcohol profile derived from 
wax esters reported a considerable variety of compounds, ranging from C lg 
to C 27 , with the C 20 chain being the most abundant. 81 Both iso- and anteiso- 
branched chain fatty alcohols were also found. In adult wax esters, the most 
common positional isomer was the A6-type, comprising 98.28% of detected 
mono-unsaturated acids. 82 Since wax esters are known to be of sebaceous 
origin, this evidence would indicate that fatty acids with the A6 double bond 
position are also of sebaceous gland origin, whereas those with A9-type are 
of epidermal origin. It was also reported that 26.7% of adult wax ester fatty 
acids were of a branched chain type. It is rare to find a wax ester that contains 
two fully saturated straight chain fatty acid components. One possible reason 
would be that the presence of unsaturation or branching makes it more likely 
that the resulting wax ester would be liquid at skin temperature. 

Sterols 

Sterol esters comprise approximately 2 to 3% of adult skin surface lipids. It 
has been proposed that sterol esters are not synthesized directly but rather 
are secondary products. 82 Two strains of bacteria, staphylococci and propi- 
onibacteria (minimally), have been found to esterify cholesterol. 83 There is 
also evidence that a major proportion of cholesterol esterification occurs on 
the skin surface. 84 Two to three times more sterols were found esterified on 
the skin surface than in the epidermis or in isolated stratum corneum. Free 
sterols are built up in the living portion of the epidermis and are then 
esterified primarily with sebum fatty acids, but also with some acids released 
from the epidermis during the late stages of keratinization. The fact that a 
high percentage of sterol esters (88.92%) have fatty acids with A6-type unsat- 
uration lends support to the hypothesis that the fatty acids comprising them 




are of sebaceous origin. 82 Approximately 20% of the fatty acids in sterol esters 
were reported to be of a branched chain type. Also, the levels of sterols and 
sterol esters have been reported to be higher in women than men. Cholesterol, 
cholest-5-en-3(3-ol, is approximately 1 to 2% of adult surface lipids. Choles- 
terol, which is the most abundant steroid in animal tissues, is not believed 
to be synthesized in the sebaceous glands. It maybe incorporated into sebum 
from the body’s circulation (e.g., blood, plasma, etc.). 

Squalene 

Squalene comprises approximately 11 to 12% of adult lipids. Squalene, 
2,6,10,15,19,23-hexamethyl-2,6,10,14,18,22-tetracosahexaene, cyclizes 
readily to form steroids in the body, including the steroid alcohols lanosterol 
and cholesterol. Squalene levels have been reported to be elevated in acne 
patients. 85 ’ 86 Patients with acne were reported to have a mean squalene con- 
tent of 19. 9%. 71 Squalene production in sebaceous glands has been found to 
vary depending on the gland size, with larger glands producing greater 
amounts of the lipid. 

Miscellaneous Organic Compounds 

A recent study of sweat collected from glass beads using cryofocusing GC/MS 
revealed a considerable number of trace organic compounds. 5 Most of the 
ketones detected were between butanone and decanone. However, trace 
amounts of the following were also found: 2-nonen-4-one, 2-decanone, 
2-methoxy-2-octen-4-one, 6,10-dimethyl-5,9-undecadien-2-one, and possi- 
bly 3-hydroxyandrostan-ll,17-dione. Numerous aldehydes were also 
detected, with the most prevalent being in the series between propanal and 
nonanal. Alkanes and alkenes below decane were not detected because of 
high volatility and amounts below instrument detection limits. Few amides 
were reported. However, a series of tertiary amines was detected ranging from 
NjN’-dimethyl- 1 -dodecanamine to N,N-dimethyl- 1 -octadecanamine. Several 
heterocyclic compounds were detected, including substituted pyrroles, 
pyridines, piperidines, pyrazines, and furans. Nicotine was also detected in 
some samples. A number of haloalkanes were reported, including an incom- 
plete series from chlorohexane to chlorohexadecane. Carbon disulfide and 
dimethyl sulfide and a few mercaptans, including thiomethane and 2-thio- 
propane, were also present. The chemical composition of secretions from the 
sebaceous gland is summarized in Table 3.6. 

Apocrine Glands 

The apocrine glands are another class of secretory glands. These glands are large 
coiled structures that are located close to hair follicles and their associated 
sebaceous glands (except where noted, the information in this section was 



Table 3.6 A Summary of the Composition of 
Sebaceous Secretions 



Organic (major) 




Organic (trace) 


Triglycerides 


30-40% 


Aldehydes 


Free fatty acids 


15-25% 


Ketones 


saturated 


50% 


Amines 


monounsaturated 


48% 


Amides 


polyunsaturated 


2% 


Alkanes 


Wax esters 


20-25% 


Alkenes 


Squalene 


10-12% 


Alcohols 


Cholesterol 


1-3% 


Phospholipids 


Cholesterol esters 


2-3% 


Pyrroles 

Pyridines 

Piperidines 

Pyrazines 

Furans 

Haloalkanes 

Mercaptans 

Sulfides 



obtained from Robertshaw 87 ). They are localized primarily in the axillary and 
perineal areas. The excretory portion of these glands takes the form of a huge 
intertwined coil that can extend well into the sub-dermal fatty layer. 2 The duct 
leaving the coil takes a more or less vertical path parallel to an adjacent hair 
follicle into which it opens at a point above the hair’s sebaceous gland. 

Few studies have been made to analyze the secretions emanating from 
the apocrine glands. Detailed analysis of apocrine secretions is complicated 
by contamination from eccrine and sebaceous glands. One of the few studies 
done on human apocrine secretions found a substance that was milky in 
appearance and dried to a plastic-like solid. 88 This material fluoresced and 
had a variable odor. One source reported several substances isolated from 
apocrine secretions, including proteins, carbohydrates, cholesterol, and 
iron. 89 C 19 -steroid sulfates and A16-steroids (e.g., 5a-androst-16-en-3a-ol 
and 5a-androst-16-en-3-one) have also been reported. 90,91 



Variation of Sebum Composition with Age of Donor 

It has been well established that the chemical content of sweat changes from 
birth to puberty and up through old age. Rates of sebum excretion, amounts 
of certain fatty acids, the ratio of wax esters to cholesterol, and cholesterol 
esters have been found to change. 92 Some components do not show any 
significant difference with age. Table 3.7 compares the variation in surface 
lipid composition by age group. 93 



Table 3.7 Changes in Surface Lipid Composition with Age 



Age 


Free 

Fatty 

Acids 


Triglycerides 


Wax 

Esters 


Cholesterol 


Cholesterol 

Esters 


Squalene 


5 days 


1.5 


51.9 


26.7 


2.5 


6.1 


9.9 


1 month-2 years 


20.8 


38.4 


17.6 


3.7 


10.3 


9.4 


2-4 years 


22.9 


49.6 


8.0 


4.2 


8.9 


6.2 


4-8 years 


15.9 


45.6 


6.9 


7.2 


14.6 


7.7 


8-10 years 


17.8 


47.4 


17.8 


3.2 


5.7 


8.3 


10-15 years 


18.8 


42.9 


23.6 


1.8 


4.2 


8.4 


18-45 years 


16.4 


41.0 


25.0 


1.4 


2.1 


12.0 



Source: Ramasastry, R, Downing, D. T., Pochi, P. E., and Strauss, J. S., Chemical composition of human 
skin surface lipids from birth to puberty, J. Invest. Dermatol., 54(2), 143, 1970. With permission. 



Newborns 

One study 94 of neonatal skin surface lipids (from vernix caseosa, a grayish- 
white substance that covers the skin of the fetus and newborn) reported the 
following lipid classes and amounts: sterol esters, 35%; triglycerides, 26%; 
wax esters, 12%; squalene, 9%; free sterols, 9%; diesters, 7%; and miscella- 
neous lipids, 4%. These values show more similarity to adult sebum profiles 
than to young children. The composition of wax ester fatty acids (with regard 
to the chain type and the amount of saturated and unsaturated) in vernix 
caseosa has been found to be quite similar to that of adults. 82 However, the 
amount of sterol esters showed considerable difference. In adults, sterol esters 
constituted approximately 2.81% of the skin surface lipids, whereas vernix 
caseosa contained 25.4%. The large percentage of high molecular weight 
sterol esters in vernix caseosa probably helps to provide a waxy coating of 
low water solubility that prevents excessive wetting of fetal skin. Fatty acids 
in vernix caseosa were predominantly saturated (65%) while adult samples 
were primarily mono-unsaturated (54%). A study of vernix caseosa by Miet- 
tienen and Lukkainen found at least eight additional sterols besides choles- 
terol, including lanosterol. 95 

The vernix caseosa of male fetuses contained much more sebum than 
those of female fetuses, which had a higher proportion of epidermal lipids. 75 
The differences were significant enough to be able to distinguish the sex of 
the fetus based on the thin layer chromatogram of lipids extracted from the 
vernix caseosa. Although androgen levels are high in newborns, the level of 
hormones (as well as sebum production) drops rapidly during subsequent 
months. 96 This leads to a dramatic change in the amount and composition 
of excreted lipids. 




Young Children 

The sebum composition of children aged 2 to 8 years old is dominated by 
epidermal lipids (e.g., cholesterol and its esters). 93 Typically, the amounts of 
wax esters and squalene in young children were measured to be approxi- 
mately one third and one half of adult levels, respectively. By the ages of 8 
to 10 years, the levels rose to about two thirds of adult levels. Adult levels 
were reached between the ages of 10 to 15 years. Median wax ester secretion 
rates were found to be between 10 to 50pg/10 cm 2 per 3-hr collection 
period. 97 Levels of cholesterol and cholesterol ester secretion were found to 
vary little between children, with the average amount secreted being 11.0 ± 
4.5 and 16.6 + 8.7 pg/10 cm 2 per 3-hr period. Another study measured the 
total sebum production rate in children. 43 The rates varied in females from 
0.60 mg lipid (per 10 cm 2 area per 3-hr period) for 7 year olds to 1.29 mg 
for 14 year olds. For males the values varied between 0.58 mg for 9 year olds 
to 2.17 mg for 16 year olds. However, in late childhood, as sebum secretion 
begins to increase, the amount of wax esters (which are of sebaceous origin) 
increased relative to cholesterol and cholesterol esters (which are of epidermal 
origin). 

There are significant changes in the relative concentrations of the major 
fatty acids constituting the triglyceride and wax ester fraction of children’s 
sebum. 98 The levels of C 15 fatty acids increased from 3% in the pre-pubertal 
group to 9% in the pubertal group. The levels of C 16:1 fatty acids increased 
to between 20 to 40% while C 18 , C 18:1 , and C 18:2 sharply declined. Also, the 
ratio of wax esters to cholesterol and cholesterol esters begins to increase 
between the ages of 7 and 8 and reaches a more “adult” profile by age 10 or 
11." Sebum secretion rates continue to increase during adolescence until 
about age 17 or 18, when a relatively stable phase is achieved. 100 Once matu- 
rity has been achieved, it appears that little changes occur in sebaceous gland 
activity until middle age. 

Adolescents 

At the onset of puberty, hormone-mediated sebaceous gland enlargement 
occurs and sebum production increases significantly. It has been suggested 
that during puberty the proportion of endogenously synthesized sebaceous 
lipids (characterized by squalene, wax esters, and A6 fatty acids) increases 
while the proportion of exogenous-type (characterized by cholesterol, A9 
fatty acids, and linoleic acid) decreases. This may be explained by the fact 
that sebaceous cells have a relatively constant amount of exogenous-type 
lipid, but they synthesize variable amounts of the endogenously synthesized 
sebaceous-type lipids. The amount synthesized is directly related to the 




gland’s activity. The more active the gland, the more dilute the exogenous 
lipids become due to excess production of sebaceous-type lipids. 

In one study, the levels of sebum production (measured as milligrams 
of lipid collected on a 10-cm 2 patch of skin over 3 hr) of subjects of varying 
age were measured. 43 The values obtained for adolescent males and females 
were 2.35 mg and 2.17 mg (per 10-cm 2 area per 3-hr period), respectively. 
The largest jump in sebum production occurred between the ages of 12 and 
13 in both males and females. The mean sebum levels differed significantly 
in certain age cohorts for subjects with and without acne. In addition, 
patients suffering from acne vulgaris were found to possess a greater amount 
of lipolytic agents than those patients without acne, which might explain the 
reported elevated fatty acid levels. 101 The difference between subject males 
aged 15 to 19 with and without acne was 2.80 mg and 1.73 mg. For females 
15 to 19, the values were 2.64 mg and 1.85 mg. In the 20 to 29 age cohort, 
the values for males were 2.87 mg and 2.37 mg; for females the values were 
2.58 mg and 1.77 mg. 

Post-Adolescence 

Sebum production continues with age, peaking during the mid thirties and 
then begins to decline in middle age. In old age, levels of sebum may drop 
to near pre-puberty levels. One study of sebaceous wax esters found that 
secretions decreased about 23% per decade in men and about 32% in 
women. 102 This is in contrast to some findings that show the rates remain 
somewhat stable. 43,103 Overall, it appears that no significant changes occur in 
sebum composition until much later in life. A study of sebum secretion rates 
of four adult males by gravimetry found a range of rates from 2.15 to 
4.47 mg/ 10 cm 2 per 3-hr period. 104 In another study, the sebum production 
rates for males and females were reported for 20 to 29 year olds, 2.48 mg and 
2.03 mg; 30 to 39 year olds, 2.52 mg and 2.04 mg; 40 to 49 year olds, 2.39 mg 
and 1.86 mg; and 50 to 69 year olds, 2.42 mg and 1.10 mg. 43 

The principal cause for the decrease in sebum gland activity with age is 
diminished hormonal stimulation. 100 Testosterone levels in men begin to 
decrease significantly between the age of 50 to 60 years. Sebaceous gland 
activity typically does not decrease until a decade or so later. In women, the 
decrease is observed a decade or so sooner than in men. The sebum produc- 
tion rates for males and females have been reported to be 1.69 mg and 
0.85 mg, respectively, for subjects over age 70. 43 Interestingly, some studies 
have shown that, although sebaceous gland activity decreases with age, the 
glands themselves become larger rather than smaller. 105 It also appears that 
with advancing age, the proportion of A9-type unsaturated fatty acids 
increases. 75 




The Composition of Latent Print Residue 



Although considerable research has been conducted on sweat samples, com- 
paratively little data are available on the content of latent print residues. The 
components of sweat transferred to different surfaces may differ from that 
found on the surface of skin. The law enforcement community began to 
examine latent print residues critically and scientifically in the late 1960s. 
The foundation work in this area was sponsored by the United Kingdom 
Home Office and conducted by the Atomic Weapons Research Establishment 
(AWRE) and the Atomic Energy Research Establishment (AERE). These 
research efforts concentrated on analyzing the chemical components of latent 
print deposits. 

United Kingdom Home Office 

The United Kingdom Home Office sponsored a considerable number of 
research projects over the past 35 years. These projects were carried out in 
cooperation with the Central Research Establishment (CRE) and the Police 
Scientific Development Branch (PSDB), which was formerly known as the 
Scientific Research and Development Branch (SRDB). These efforts repre- 
sented, in many cases, the first attempt to perform a detailed study and 
analysis of visualization methods as well as the composition of print residue. 

During the mid to late 1960s, a series of projects were done to investigate 
the organic and inorganic substances present in a latent print. One study 
examined the water soluble components and reported the following sub- 
stances (and approximate amounts): chloride, 1 to 15 pg; calcium, 0.03 to 
0.3 pg; sulfur, 0.02 to 0.2 pg; urea, 0.4 to 1.8 pg; lactic acid, 9 to 10 pg; amino 
acids, 1 pg; phenol, 0.06 to 0.25 pg; sodium, 0.2 to 6.9 pg; potassium, 0.2 to 
5.0 pg; and ammonia, 0.2 to 0.3 pg. 106 A subsequent study examined the 
change in chloride content in fingerprints as a factor of the donor’s age. 107 
Results indicated that the chloride content decreased with advancing age. In 
addition, the donor’s occupation also appeared to be a factor. Office workers 
were found to have the highest amounts of chloride followed by laboratory 
workers and persons employed in workshops. Differences were also found 
between left and right hands as well for individual fingers. Statistically, digits 
on left hands were found to have a higher chloride content, presumably 
because most of the donors were right handed. Thumbs had the lowest 
amount of chloride while little fingers had the highest. However, because of 
a significant variation present within the same individual, these trends were 
not always observed. 

The Home Office also conducted detailed studies of the lipid (or water- 
insoluble) portion of latent prints, with an emphasis on the free fatty acid 




content. 108 Palmitic acid was found to be the most abundant fatty acid. In 
general, the most abundant acids were C 18 /C 18:1 + squalene followed by 
Cj 6 /C I6:I , C 14 /C 14:1 , C 15 , and C 12 /C 12:1 . Another study confirmed that palmitic, 
stearic, and palmitoleic acids were the most abundant fatty acids. 72 This study 
also addressed the contribution of cosmetics present in samples from female 
volunteers. They found that the presence of cosmetics might introduce peaks 
in the early portion of the chromatogram (e.g., decanoic acid). The mean 
values obtained for the amounts of the various lipid classes found in forehead 
samples are reported in Table 3. 5. 72 Those values can be compared with the 
following average values obtained from fingers: squalene, 14.6%; cholesterol, 
3.8%; free fatty acids, 37.6%; wax esters (with diglycerides), 25%; and tri- 
glycerides (with monoglycerides and cholesterol esters), 21%. Although some 
differences are to be found in the free fatty acid and glyceride values, these 
discrepancies can be attributed to individual variations in bacterial lipase 
activity. Additional studies, using gas-liquid chromatography, detected over 
40 different organic constituents in sebaceous secretions. The results, 
expressed as general lipid classes, are reported in Table 3. 5. 3 The report 
stressed that the sebaceous secretions are very important with regard to 
fingerprint visualization because they are more stable to water than the 
principal components of eccrine sweat. 

Oak Ridge National Laboratory 

A 1993 child abduction case in Tennessee inspired a local police criminalist 
and a chemist from the Oak Ridge National Laboratory (ORNL) to team up 
and analyze fingerprint residues. 109111 Knoxville Police criminalist Art Boha- 
nan observed that children’s fingerprints left on nonporous surfaces (such as 
a vinyl car seat) did not seem to last for more than a day or two. Subsequent 
analyses performed by Buchanan et al. at ORNL indicated a significant dif- 
ference in the chemical composition of children’s and adults’ print resi- 
dues. 112,113 Children’s prints contained more volatile components that would 
not remain in the deposit for more than a couple of days (depending on the 
environmental conditions). In both children and adults, fatty acids (as methyl 
esters) in the C 12 to C 24 range were detected. Although cholesterol was found 
in prints from children and adults, the amount was significantly higher in 
children. There were differences detected between samples from male and 
female children, although these compounds were not identified. The most 
abundant compound detected in the isopropyl alcohol extracted material of 
adults was squalene. In addition, several long chain fatty acid esters were 
identified, including pentadecanoic acid dodecyl ester, and the undecyl, tride- 
cyl, pentadecyl, heptadecyl, and octadecyl esters of hexadecanoic acid. 



Subsequent studies conducted at the ORNL yielded some unusual 
results. 114 Nicotine was detected in some of the adult samples. Although 
initially dismissed as environmental contamination caused by handling 
tobacco products or exposure to second-hand tobacco smoke, a subsequent 
analysis of a sample obtained from an individual who had quit smoking 
several weeks before (but had been chewing nicotine gum) showed traces of 
nicotine. While unexpected, this result is not unprecedented. Robinson et al. 
reported the presence of nicotine, as well as morphine and alcohol, in sweat 
in 1954. 115 Traces of steroids were also observed in some of the fingerprint 
samples. ORNL plans to direct future efforts toward the ability to detect trace 
amounts of special target compounds (e.g., illegal drugs and their metabolites) 
in latent print residues to provide investigative leads for law enforcement 
purposes. If successful, such noninvasive methods could potentially eliminate 
the need to obtain biologically hazardous samples such as blood or urine. 

Pacific Northwest National Laboratory 

With funding obtained from the Technical Support Working Group (TSWG 
is an interagency working group that funds counter terrorism projects), the 
U.S. Secret Service (USSS) teamed up with the Pacific Northwest National 
Laboratory (PNNL) to conduct a research project to investigate the compo- 
sition of latent print residue. The most critical aspect of this project was to 
investigate how latent print residue changes over a period of time. Fingerprint 
samples from 79 volunteers, ranging in age from 3 to 60 years old, were 
analyzed. Volunteers placed fingerprints on filter paper samples. The samples 
were then stored at ambient conditions before being extracted. After deriva- 
tization, the samples were analyzed by gas chromatography/mass spectrometry. 

The results of this study were in agreement with the data obtained at the 
ORNL. 116 Several samples analyzed appeared to be contaminated by external 
sources of lipids, such as hand lotions, cosmetics, and soaps. Removing all 
traces of these contaminants proved difficult. The data obtained from the 
aging of fingerprint residues were also reported. As expected, most of the 
unsaturated lipids (e.g., squalene and fatty acids such as oleic and palmitoleic) 
tended to diminish substantially within the 30-day period, with significant 
losses during the first week noted. Since lipids like squalene and oleic acid 
are liquid at room temperature, they provide an environment suitable for 
partitioning of certain lipid-specific visualization reagents. Once they have 
been modified and the majority of the water content of the print has evap- 
orated, the print dries out and is no longer amenable to lipid partitioning 
reagents. For example, reagents like Nile red, which partition into the lipid 
layer, are generally ineffective on prints more than a few days old. 





Figure 3.4a A chromatogram of a fingerprint deposit extracted and analyzed 
shortly after deposition. 



In contrast, saturated compounds (e.g., palmitic and stearic acids) 
remained relatively unchanged during the same time period. Wax esters also 
remained relatively stable. Overall, as the sample fingerprint aged, com- 
pounds in the low molecular weight range began to form. These compounds 
would be consistent with lighter molecular weight saturated acids (e.g., 
nonanoic acid) and diacids (e.g., nonandioic acid). Figures 3.4a and 3.4b are 
chromatograms of samples taken from the same donor and analyzed initially 
and 60 days later. Overall, the results of the study indicate that saturated 
compounds dominate aged samples. Unfortunately, these compounds do not 
make good targets for chemical reagents. 



Abundance 
8000000 h 



TIC: 102008. D 




Figure 3.4b A chromatogram of the same fingerprint deposit extracted and ana- 
lyzed 60 days after deposition. 



Savannah River Technical Center Research 

Another project was recently begun at the Savannah River Technical Center 
(SRTC) in cooperation with the USSS to analyze latent print residue and how 
it changes with time. With funding from both the TSWG and Department 
of Energy, the SRTC is looking into characterizing the degradation products 
formed as the latent print residue ages to determine if any of these com- 
pounds may be suitable for chemical visualization reagents. The SRTC is 
focusing on the formation of hydroperoxides, one class of breakdown prod- 
ucts formed as lipids oxidize. A series of standard lipids representative of the 





various lipid classes found in a latent print was used. These included com- 
pounds typically found in print residue, including cholesterol, triglycerides, 
fatty acids, wax esters, cholesterol esters, and catalyze the reaction between 
triplet a sensitizer (protoporphyrin IX dimethyl ester, 0.01% of the overall 
mixture). The sensitizer was added to oxygen and light to form singlet oxygen 
(a highly reactive species). These compounds were placed on a glass slide 
and aged in various conditions (e.g., light/no light and/or indoors/outdoors). 
Like PNNL, the SRTC found that unsaturated compounds are rapidly 
depleted from samples even in cool, dark storage conditions. An experiment 
involving the aging of squalene on a glass slide found that after one month 
of exposure to ambient conditions, 10% of the sample was composed of 
hydroperoxides. The SRTC is looking into chemiluminescent methods for 
visualizing the hydroperoxides formed as fingerprints age. 

Forensic Science Service 

Recent work done at the Home Office Forensic Science Service (FSS), Met- 
ropolitan Laboratory, London, England, involved the use of thin layer chro- 
matography (TLC) to directly separate sebum-rich fingerprints from five 
donors left on TLC plates. 117 The FSS has recently updated this work. 118,119 
Although the use of TLC to analyze latent print residues is not new, 120 ’ 121 the 
direct separation and characterization of a deposited print was unique. The 
ultimate goal of these experiments was to react the separated classes of latent 
print residue with different chemical reagents. Additional studies are being 
planned in cooperation with the Police Science and Criminology Institute, 
University of Lausanne, Switzerland. In addition, the FSS has been working 
on trying to identify the compound(s) responsible for inherent luminescence 
observed in some latent prints. Efforts using TLC, GC/MS, and Raman 
spectroscopy have not provided a definitive answer, but one leading candidate 
is bilirubin. The FSS suggested that bacteria, present on the skin, might be 
involved. Bacteria are known to produce porphyrins (intermediates in the syn- 
thesis of heme), which fluoresce in the visible region. The most likely candidate 
for inherent luminescence, bilirubin, is the breakdown product of heme. 

Currently, a collaborative effort, funded by the TSWG, is underway 
between the USSS and FSS to investigate the effect of light conditions on the 
aging of print residues. The project will analyze samples from five male 
donors, aged 24 to 34, at a sampling interval of 0 (shortly after deposition), 
3, 7, 9, 10, 15, and 20 days. The samples will also be cut in half and then 
subjected to different lighting conditions while at constant temperature and 
humidity. Although the study is not complete, some of the initial results are 
consistent with data generated by PNNL. There appear to be significant differ- 
ences in decomposition rates for samples in the different lighting conditions. It 




would be of interest, if future funding is available, to evaluate the impact of 
other environmental conditions on latent print decomposition products and 
rate. 

DNA From Latent Prints 



Another important component of latent print residue is deoxyribonucleic 
acid (DNA). It is not surprising that a significant amount of DNA is often 
present in visible blood prints. However, it can also be deposited in non- 
blood latent print residue from the epidermal cells that are continuously 
sloughed off the skin surface through rubbing of the skin or through direct 
contact with a substrate. In the past, an examiner was often forced to decide 
what evidence is more important, the DNA or the ridge detail. Advances in 
DNA technology have made this decision easier since fewer latent print 
visualization processes inhibit sample analyses. The use of polymerase chain 
reaction (PCR) analysis has allowed subnanogram quantities of DNA to be 
detected, amplified, and analyzed. In addition, “lab on a chip” technology 
will soon allow for extremely fast analysis and identification at the crime 
scene. 122 ' 125 Examiners are now also able to extract DNA in situations previ- 
ously considered improbable. Sweet et al. reported that identifiable DNA was 
obtained from a bite mark on skin from a victim who had been drowned. 126 
Such advances will begin to highlight the need to rapidly and reliably extract, 
analyze, and identify DNA recovered from latent prints. 

DNA From Blood Prints and Stains 

The recovery of DNA from visible blood prints and latent blood prints 
developed by chemical reagents has been well documented. Most studies 
found that only a few visualization reagents inhibit DNA analysis. A study 
of envelopes, stamps, and cigarette butts by Presley et al. using Chelex extrac- 
tion and PCR HTA DQ alpha typing found negative DNA results after pro- 
cessing with PD. 127 A subsequent study by Walls also found that physical 
developer adversely affected DNA analysis. 128 However, it was reported that 
the problem with PD could be overcome by using organic extraction rather 
than Chelex. Stein et al. studied the effect of black powder, ninhydrin, 
cyanoacrylate fuming, and gentian violet on 1-, 14-, and 56-day-old blood- 
stains and saliva samples. They found that none of the latent print visualiza- 
tion treatments adversely affected DNA extraction, quality, or typing using 
restriction fragment length polymorphism (RFTP) or PCR-short tandem 
repeat (STR). 129 Another study examined the effects of cyanoacrylate (CA) 
fuming and forensic light sources on bloodstains with subsequent analysis 





of DNA using RFLP. 130 No adverse effects were reported. Newall et al. inves- 
tigated the effect of CA fuming on blood prints and also found no inhibi- 
tion. 131 Another light source study was conducted by Andersen and 
Bramble. 132 They found that exposure of DNA to 255-nm shortwave UV 
radiation (1 mW/cm 2 at a distance of 25 to 35 cm) for as little as 30 sec could 
drastically reduce the chances of recovering and identifying DNA using PCR- 
STR analysis. 

A study of the effect of seven different blood reagents (amido black, DFO, 
ninhydrin, Hungarian Red, Crowle’s Double Stain, luminol, and Leucomal- 
achite Green) on DNA recovered from diluted blood prints on several porous 
and nonporous substrates and analyzed using the PCR-STR/Profiler Plus 
multiplex system found no adverse results. 133 Miller reported success with 
these reagents with a blood dilution factor of up to 1:10, 000. 134 The report 
also mentioned that as the length of exposure to the reagents and the extent 
of dilution of the blood sample increased (beyond 1:10,000), the possibility 
of recovering DNA diminished significantly. A similar result for luminol was 
reported by Gross etal. 135 Champod reported on PCR-STR analysis work 
done by Brignoli and Coquoz that found difficulties with LMG and o-toli- 
dine, but not with MMD. 136 Hochmeister et al. reported a similar result for 
LMG and o-tolidine using RFLP analysis. 137 Roux et al. also looked at the 
effect of visualization reagents on blood prints. 138 MMD, magnetic finger- 
print powder, and UV radiation were found to interfere with PCR DNA 
analysis. The study also found that DFO, Sticky-side powder, ninhydrin with 
secondary metal salt treatment, amido black, diaminobenzidine, luminol, 
CA with rhodamine 6G, and black powder could adversely affect recovery 
and analysis of DNA using the D1S80 system primers. Most of these problems 
were resolved by using CTT system primers. Their study also indicated prob- 
lems with the blood reagent benzidine dissolved in glacial acetic acid. 

DNA From Developed Latent Prints 

Very few studies have been published that examine the possibility of recov- 
ering DNA from treated latent prints (rather than treated bloodstains or 
blood prints). Recently, Zamir et al. investigated the effect of DFO treatment 
of latent prints on DNA analysis and found that it had no adverse effect. 139 
Another related issue involves the possibility of recovering DNA from unde- 
veloped fingerprints left on commonly handled objects. This issue was high- 
lighted by van Oorschot and Jones in the journal Nature in 1997. 140 The 
quantity of DNA recovered from objects like a car key, briefcase handle, and 
a telephone handset was found to be sufficient to identify the person who 
had handled the item. In some cases DNA transferred from another source 
(a secondary transfer) was detected and identified. However, a similar study 




done by the Royal Canadian Mounted Police (RCMP) found that such sec- 
ondary transfers can occur but are rare. 141 Another study by Ladd et al. found 
that primary transfer was not always detected and that no secondary transfer 
occurred with their samples. 142 

A subsequent letter in Nature reported success in using PCR-STR to 
obtain profiles from single cells using six forensic STR markers. 143 DNA was 
successfully amplified in 91% of the cells tested and a full DNA profile was 
obtained in 50% of those cases. This sort of success ultimately leads to the 
question of whether DNA could be recovered from a smeared or partial, 
developed print that was not of identification value. Two issues are critical. 
Do latent prints contain a sufficient number of cells and what effect do all 
of the latent print visualization techniques have on DNA analysis? Two 
projects funded by the TSWG in cooperation with the USSS are currently 
underway to begin exploring both concerns. Dr. Mark Batzer, from The 
Louisiana State University Medical Center (LSUMC), New Orleans, LA, is 
working on quantifying the amount of cellular material present in a latent 
print as well as using nuclear DNA methods to analyze and identify it. Dr. 
Robert Bever, of the Bode Technology Group, Springfield, VA, is working on 
optimizing mitochondrial DNA (mtDNA) techniques for partial latent 
prints. Since there are inherently several orders of magnitude more copies of 
mtDNA present in a cell, the likelihood of finding it is better in very small 
or degraded samples. 

DNA is also capable of yielding more than just a strict identification or 
elimination of a suspect. The sex and geographic origin of the individual can 
now be determined from DNA. 144 - 146 DNA markers that can yield information 
about hair color, height, and other morphological characteristics are also 
being explored. This was evident at the recent Millennium Conference on 
Forensic Human Identification sponsored by the Forensic Science Service, 
which was held in London in October 1999. 147 1 50 Interestingly, this technol- 
ogy is likely to be involved in settling a controversy surrounding Beethoven’s 
origin. 151 



Miscellaneous Compounds and Contaminants 

Many environmental contaminants have been detected both in analyses of 
sweat and fingerprint residues. Caution must be exercised in determining 
whether such compounds might indeed be contaminants or as compounds 
derived from an endogenous source. There may be some overlap between 
compounds present in the contaminant and ones from an endogenous 
source, which could lead to overestimates of the quantity of such compounds. 
Bernier et al. reported a significant amount of glycerol in one sample. 5 This 




was later found to be caused by the use of hair gel by one of the volunteers. 
Benzene, toluene, styrene, and alkyl substituted benzenes were also detected 
but considered as exogenous contaminants. A number of siloxanes, believed 
to be related to the column stationary phase, and phthalates were also 
detected. Hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane were 
the two primary siloxane compounds. In addition, 1,1-difluoroethane was 
one of the most intense peaks detected. This compound is a component of 
Dust-Off, a product used to cool the glass injection port liner between runs. 

The study by PNNL also detected several exogenous contaminants, 
including acetaminophen and n-butylphenylsulfonamide, a detergent found 
in gasoline. A number of hydrocarbons and glycerol esters were detected and 
attributed to contamination by cosmetics or other personal hygiene products. 
Typical examples of contaminant hydrocarbons include a series from tri- 
cosane to nonacosane, eitriacontane, and dotriacontane. Examples of esters 
include the 3,4-methoxyphenyl-2-ethylhexyl ester of propenoic acid and glyc- 
eryl trioctyl ester. 



Conclusions 



Latent print residue is a complex mixture of many different types of substances. 
Derived primarily from the three major secretory glands, sweat is deposited on 
virtually every surface touched by hands. Future efforts must continue to focus 
on determining how latent print residue adheres to, interacts with, and changes 
with time on different surfaces. This information is critical to understanding 
not only how reagents used to visualize latent prints work, but also to provide 
better guidance in modifying existing reagents and developing new ones. 

Interestingly, there have been efforts in this past decade by several labo- 
ratories to produce “artificial sweat.” Both the German Bundeskriminalamt 
(BKA) and the FSS have worked on creating a way of reproducibly creating 
a standard latent print. The applications for such a “standard latent print” 
are numerous. With the advent of laboratory accreditation guidelines estab- 
lished by organizations such as the American Society of Crime Laboratory 
Directors (ASCLD-LAB) and the International Organization for Standard- 
ization (ISO), the use of a “standard latent print” becomes critical in evalu- 
ating the effectiveness of visualization reagents that are routinely used in the 
evidence processing laboratory, as well as in the area of comparative testing 
and evaluation of new reagents worldwide. In the near future, the TSWG will 
be providing funding to build upon the groundwork established by the BKA 
and FSS. This project will also take advantage of the knowledge gained by 
the recent research efforts that have examined the chemical composition of 
recent and aged latent print residues. 




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Methods of Latent 
Fingerprint Development 

HENRY C. LEE 
R.E. GAENSSLEN 




Contents 



Introduction 
Powder Dusting 

Regular Fingerprint Powders 

Traditional Fingerprint Powders 
Organic Fingerprint Powders 
Luminescent (Fluorescent and Phosphorescent) 

Fingerprint Powders 

Metallic (Magnetic, Fine Lead, and Metal Evaporation) 
Fingerprint Powders 
Thermoplastic Fingerprint Powders 

Casting of Plastic Fingerprints/Recovery by Casting Methods 
Small Particle Reagent and Variants 
Chemical Fuming and Enhancement 
Iodine Fuming 

Iodine Fuming Gun Method 
Iodine Fuming Cabinet Method 
Iodine Dusting Method 
Iodine Solution Method 
Cyanoacrylate (Super Glue) Fuming 
Cyanoacrylate Fuming Procedure 
Fume Circulation Procedure 
Heat Acceleration Procedure 
Chemical Acceleration Procedure 
Vacuum Acceleration Procedure 
Other Acceleration Procedures 

Further Enhancement and Post -Treatment Procedures 
after Cyanoacrylate Processing 

Gentian Violet Solution — Phenol Containing 
Formulation 

Gentian Violet Solution — Non-Phenol Formulation 



Coumarin 540 Dye Staining Method 
Androx Dye Staining Method 
Other Dyes and Dye Mixtures 
Rare Earth Complexes 

Fluorescent and Other Chemical Fuming/Treatment Procedures 
Ninhydrin and Chemical Alternatives 
Ninhydrin 

Pre-Treatment and Post-Treatment Techniques for the 
Enhancement of Ninhydrin-Developed Patent Prints 
Chemical Alternatives to Ninhydrin 

Reagents for Detection of Amino Acids 
Ninhydrin Analogues 

Development of Patent Prints With Metal Ions/Compounds — 
Physical Developers 

Silver Nitrate Reagent 

Other Silver-Containing Compounds 

Physical Developer 

Modified Physical Developer Methods 
Metal Deposition 
Special Surfaces or Situations 

Enhancement of Bloody Fingerprints 
Development of Latent Prints on Tape or Sticky Surfaces 
Detection of Latent Prints on Skin 
Development of Latent Fingerprints on Wet Surfaces 
Development of Latent Fingerprints on Other Special Surfaces 
Luminescence/Fluorescence — Laser and Alternative Light Source 
Methods for Latent Print Enhancement 

Laser Light and Alternative Light Sources 
Miscellaneous Methods 

Systematic Approaches to Latent Print Processing 
References 



Introduction 



Fingerprints have often been and still are considered one of the most valuable 
types of physical evidence in identification. A complete discussion of the 
history and development of fingerprints and their use in identification is 
presented in Chapter 1. There are, in general, three forms of fingerprint 
evidence that may be found at a crime scene: visible (or patent) prints, 
impression (or plastic) prints, and latent prints. This chapter is mainly con- 
cerned with latent prints, which, as the name suggests, are ordinarily invisible 



or less visible and thus require some means of development or enhancement 
for their visualization. Over time, many investigators have explored new and 
improved techniques for the development and recovery of latent prints. In 
more recent years, new dimensions have been opened in latent print pro- 
cessing techniques, revolutionizing the field of fingerprint identification. New 
techniques have been developed not only for latent fingerprint detection, but 
also for fingerprint identification. These developments have significantly 
improved the efficiency of criminal investigation and personal identification. 

In the past, powder dusting, ninhydrin spraying, iodine fuming, and 
silver nitrate soaking were the four most commonly used techniques of latent 
print development. 1 4 These conventional techniques are quite effective in the 
recovery of latent prints under many ordinary circumstances. However, latent 
prints can be deposited on objects or surfaces with unique characteristics: 
wet surfaces, surfaces with multicolored backgrounds, surfaces contaminated 
with blood or other body fluids, objects with unusual shapes or contours, 
waxed surfaces, fabrics or untreated wood, varnished surfaces, human skin, 
cardboard boxes, and other porous or nonabsorbent surfaces. Under these 
conditions, traditional methods of latent print detection are often ineffective. 
At times, application of the wrong techniques may even result in the destruc- 
tion of potential latent print evidence. 

For years, fingerprint scientists have sought new methods or tried to 
improve existing methods for the visualization of latents. At an overall level, 
all successful methods of latent print enhancement are targeted toward some 
known component of latent print residue (see Chapter 3). Although a com- 
plete understanding of all individual components in latent print residue and 
their quantities has not been attained, many of the compounds present are 
known. Some methods target water-soluble components while others target 
lipids. The best method, then, depends on the latent, the surface, and any 
environmentally induced changes. At another level, enhancement methods 
exploit the chemistry of latent residue components and their potential reac- 
tions and interactions. Efforts have focused on the development of techniques 
that may be successfully applied to unique and difficult surfaces and that 
offer increased sensitivity over conventional techniques. The newer proce- 
dures can be divided into three major categories: (1) new chemical reagents 
for latent print visualization; (2) optical and illumination methods for the 
development or enhancement of latent prints; (3) combinations of chemical 
and illumination methods. Finally, there are systematic approaches, involving 
not only combinations of methods, but careful consideration of their order 
of application. Some of these areas have been periodically reviewed, e.g., by 
Pounds, 5 Goode and Morris, 6 Hazen, 3 Lee and Gaensslen, 7 and Lennard and 
Margot. 8,9 In this chapter, we discuss the various physical, chemical, and 
illumination methods and systematic approaches for the enhancement and 




visualization of latent fingerprints, and also provide some of the reagent 
formulations and procedures used. 



Powder Dusting 

The simplest and most commonly used procedure for latent fingerprint devel- 
opment is powder dusting. Powder dusting is a “physical” method of enhance- 
ment that relies on the mechanical adherence of fingerprint powder particles to 
the moisture and oily components of skin ridge deposits. Application of powder 
to latent prints by brushing is a simple technique and yields instantly apparent 
prints, but it also has disadvantages. Contact of the brush with the fingerprint 
ridges has an inevitably destructive effect. The use of fingerprint powders dates 
back to the early nineteenth century. In general, there are four classes of finger- 
print powders: regular, luminescent, metallic, and thermoplastic. 

Regular Fingerprint Powders 
Traditional Fingerprint Powders 

Regular fingerprint powders consist of both a resinous polymer for adhesion 
and a colorant for contrast. Hundreds of fingerprint powder formulas have 
been developed over the years. A detailed discussion of fingerprint powder 
formulas and their preparations can be found in the first edition of Scott’s 
Fingerprint Mechanics 1 and in the report by Goode and Morris. 6 Following 
are some of the most commonly used fingerprint powder formulas: 

Black Fingerprint Powder Formulas: 



Ferric oxide powder 

Black ferric oxide 50% 

Rosin 25% 

Lampblack 25% 

Manganese dioxide powder 

Manganese dioxide 45% 

Black ferric oxide 25% 

Lampblack 25% 

Rosin 5% 

Lampblack powder 

Lampblack 60% 

Rosin 25% 

Fuller’s earth 15% 




White Fingerprint Powder Formulas 



Titanium oxide powder 



Titanium oxide 


60% 


Talc 


20% 


Kaolin lenis 


20% 


Chalk-titanium oxide powder 


Chalk 


15% 


Kaolin lenis 


15% 


Titanium oxide 


70% 


Gray Fingerprint Powder Formulas 


Chemist gray powder 


Chemist gray 


80% 


Aluminum powder 


20% 


Lead Carbonate Powder 


Lead carbonate 


80% 


Gum arabic 


15% 


Aluminum powder 


3% 


Lampblack 


2% 



In addition, there are many different types of colors or metallic finger- 
print powders commercially available. Some of the chemical substances used 
in fingerprint powders are toxic or pose other potential health hazards, 
including antimony trisulfide, antimony powder, cobalt oxide, copper pow- 
der, cupric oxide, lead carbonate, lead iodide, lead oxide, lead sulfide, man- 
ganese dioxide, mercuric oxide, mercuric sulfide, tin powder, and titanium 
dioxide. Safety procedures and caution should be exercised when preparing 
or using powders containing these chemicals. 

In recent years, researchers have further improved the mechanism and 
technique of powder dusting latent fingerprints by coating the fingerprint 
powder onto fine quartz powder and/or small plastic particles. Different sizes 
of fingerprint powder-coated particles can be used for different purposes in 
processing. The following are some of the basic formulations used by BVDA 
Inc., The Netherlands, in their particle-coated fingerprint powders: 

Silver powder Aluminum flake, quartz powder 

Gold powder Bronze flake, quartz powder 

Black powder Iron oxide, quartz powder, kaolin, carbon soot 




White powder Dolomite, starch powder 

Gray powder Kaolin, aluminum flake powder 

The following factors should ordinarily be considered in the selection of 
a fingerprint powder: 

1 . The surface should be suitable for powder dusting and not itself attrac- 
tive to fingerprint powder (such as polyethylene). 

2. The color of the fingerprint powder should be selected to give maximum 
contrast with the surface on which the latent print was deposited. 

3. The powder must adhere well to the deposits left by the friction skin 
ridges of a finger or palm. 

4. The particle size of the powder should be fine enough to yield good, 
clear ridge patterns. 

Generally, fingerprint powder is applied to the surface bearing the latent 
print with a fingerprint brush. These brushes are distinguished according to 
the types of fibers used to make them. Occasionally, powder can be applied 
to the surface by means of an atomizer, aerosol spray, or electrostatic appa- 
ratus. 

When applying powder with a fingerprint brush, extreme care should be 
taken to avoid damaging the latent print. Valuable fingerprint evidence is 
occasionally destroyed by carelessness in the application of powder. James 
et al. have looked carefully at this problem and recommended techniques 
and types of brushes for best avoiding it. 10 The following is a generalized 
procedure for developing latent prints with fingerprint powder: 

1. Visually search the surface to identify possible latent print deposits. 

2. If a fingerprint is found, it should be photographed using an appro- 
priate photographic technique. 

3. Select an appropriate fingerprint powder and brush. When in doubt, 
make a test print to help in choosing the best powder and brush for 
the circumstances. 

4. Carefully apply the powder to the surface with a light brushing action. 

5. Remove the excess powder by dusting the surface with a gentle, smooth 
motion until the best fingerprint image has been developed. 

6. Photograph useful fingerprints in situ. The photograph should contain 
all the necessary case information and the latent print number. 

7. Apply a suitable fingerprint lifting tape and carefully lift the powdered 
latent print from the surface. 

8. Examine the latent lift and if necessary reprocess or relift the original 
latent print. 




An alternative technique was proposed by Barron, Haque, and Westland 11 in 
which a freeze and thaw method was used before dusting with fingerprint 
powder. James et al. milled aluminum-based and other powders to determine 
the optimal particle size (5 to 10 pm long and 0.5 pm thick) and stearic acid 
content (3 to 5%) for latent fingerprint development. 12 

A variation on the usual powder dusting procedures, but which can 
nevertheless be considered a kind of “powder” development technique, was 
described by Waldock. 13 A camphor candle was used to produce soot that 
could “coat” the latent print. 

Organic Fingerprint Powders 

Many commercial fingerprint powders contain toxic inorganic chemicals 
such as lead, mercury, cadmium, copper, silicon, titanium, and bismuth. 
Long-term exposure to them may present a health hazard. The use of organic 
fingerprint powders for latent print dusting was suggested by Kerr, Haque, 
and Westland. 14 A typical powder formula consists of the following: 

Potassium bromide 1 g 

Cornstarch 35 g 

Distilled water 25 mL 

The procedure that was used to prepare the organic fingerprint powder 
was as follows: 

1. Dissolve 1 g potassium bromide in 25 mL distilled water. 

2. Slowly dissolve 35 g cornstarch in the above solution with constant 
stirring. 

3. Dry the cornstarch mixture at room temperature for 7 days. 

4. The solid mass is periodically ground with a mortar and pestle over 
the drying period to produce a finer powder. 

5. The powder is stored in a tightly stoppered container containing anhy- 
drous calcium sulfate as a desiccant. 

It was reported that cornstarch-based fingerprint powders yielded excellent 
results in developing latent prints on nonporous surfaces. In addition to 
regular cornstarch fingerprint powders, the same research group also 
reported on the use of organic-based fluorescent powders for latent print 
detection. 15 The following are several organic-based fluorescent fingerprint 
powders as reported by Kerr et al.: 15 



Calcium sulfate 
Dihydrate cornstarch 



5-10% 

90-95% 




Fluorescein solution (in methanol/water) 1% 

Barium sulfate 5% 

Flour 5% 

Titanium dioxide 0.5% 

Cornstarch 89.5% 

Fluorescein solution (in methanol/water) 1% 

Gum arabic 2% 

Cornstarch 98% 

Rhodamine B (aqueous solution) 2% 

Cornstarch 100% 

Fluorescein solution (in methanol water) 1% 



Luminescent (Fluorescent and Phosphorescent) 

Fingerprint Powders 

Many types of powders contain natural and/or synthetic compounds that 
fluoresce or phosphoresce upon exposure to ultraviolet (UV) light, laser light, 
and other light sources. These types of fingerprint powders are useful for the 
visualization of latent prints deposited on multicolored surfaces that would 
present a contrast problem if developed with regular fingerprint powder. 
Luminescent fingerprint powders have rarely been used in the field. With the 
advent of laser detection, however, it was found that dusting the latent prints 
with fluorescent or phosphorescent powders greatly enhanced laser exami- 
nation. Acridine yellow, acridine orange, coumarin 6, crystal violet, p,p'- 
dichlorodiphenylmethyl carbinol, 3,3 '-diethyloxadicarbocyanine iodide, 
3,3 / -diethylthiotricarbocyanine iodide, merocyanine 540, Nile Blue perchlo- 
rate, Rhodamine B, Rhodamine 6G, phenothiazine, and many other lumi- 
nescent dyes and pigments have been reported to be useful as luminescent 
dusting powders for laser examination. Selection of the most satisfactory 
powder is largely dependent on the background colors and their luminescent 
properties. Good results have been reported with several formulations. 16-20 

Metallic (Magnetic, Fine Lead, and Metal Evaporation) 

Fingerprint Powders 

Magnetic powders are fine ferromagnetic powders that are applied by use of 
a magnetic applicator. This method was first reported by MacDonell. 21 It was 
found that magnetic powders are particularly successful in the recovery of 
latent prints from surfaces such as leather, plastics, walls, and human skin. 
The magnetic powder process has also been widely used for processing latent 
prints on vertical surfaces. The basic materials used in magnetic powder are 
iron oxide and iron powder dust along with other coloration compounds. 
Magnetic flake powders developed by James and collaborators 22 have been 
shown to be equal or superior to classical “magna” powders in developing 




latent fingerprints. 23 The new powders no longer contain magnetic particles 
to serve as the “brush” and nonmagnetic particles to adhere to the print 
residue. In addition, fine lead powder has been used for latent print detection 
with X-ray electronography and autoelectronography. 24 Cadmium, zinc, and 
gold/zinc metals have also been used in vacuum metal deposition techniques 
for latent print detection. 25,26 These procedures are discussed below. 

Thermoplastic Fingerprint Powders 

Thermoplastic powder-dusting techniques involve powders such as photo- 
copier toners or dry inks. 27,28 Latent fingerprints developed with such mate- 
rials become fused to the surface upon exposure to heat. 

Casting of Plastic Fingerprints/Recovery by Casting Methods 

Stimac 29 noted that the processing of plastic (or “indentation”) prints is not 
commonly discussed. He described a casting method similar to what might 
be used for fine tool marks, followed then by the use of the resulting cast to 
make an inked impression for comparison. Feucht 30 described the use of 
polyvinylsiloxane dental impression materials to recover latent prints from 
rough surfaces including ceiling tiles, safes, and paper currency. 



Small Particle Reagent and Variants 

The small particle reagent technique relies on the adherence of fine particles 
suspended in a treating solution to the fatty or oily constituents of latent 
fingerprint residue. Accordingly, it may be regarded as belonging to the same 
family of methods as powder dusting. Small particle reagent (SPR) consists 
of a suspension of fine molybdenum disulfide particles in detergent solution. 
The particles adhere to the fatty constituents of latent print residues and 
form a gray molybdenum disulfide deposit. This method was first reported 
by Morris and Wells. 31 A detailed procedure and formulation were described 
later by Goode and Morris. 6 Pounds and Jones 32 reported that choline chlo- 
ride was not an essential component of the formulation. They recommended 
the use of molybdenum disulfide dispersed in Manoxol OT. 

The following is one formulation and procedure used for developing 
latent prints with small particle reagent: 

Reagents 

Molybdenum disulfide (MoS 2 ) 30 g 

Distilled water 1 L 

Photo Flo 200 see below 




Notes: Dissolve the MoS 2 in the distilled water. Add 3 drops of the Photo Flo 200 and 
shake the solution well to ensure that the molybdenum disulfide has gone into 
solution. This solution has a shelf life of about 6 to 8 weeks. 

Spraying Procedure: 



1. Shake the reagent solution thoroughly and fill a spray bottle with it. 

2. Spray the SPR onto the area to be searched for latent prints. Shake the 
bottle between sprayings to prevent the molybdenum disulfide from 
settling to the bottom. 

3. Using a separate spray bottle with clean water, rinse the searched area 
to remove the excess SPR reagent. 

Dipping Procedure: 



1 . Mix the reagent solution thoroughly and fill a photographic processing 
tray with it. 

2. Rock to mix the solution thoroughly, and immerse the evidence item 
in it. Particles of MoS, will settle on the surfaces where latent prints 
are likely to be located. 

3. Repeat the treatment with the other side of the evidence item. 

4. After 2 min, carefully remove the evidence item and rinse gently with 
clean water. 

The developed latent print appears as a dark to light gray color. The SPR 
solution has been successfully used to develop latent prints on paper, card- 
board, metal, rusty metal, rocks, concrete, plastic, vinyl, wood, and glass. 
Similarly, latent prints have been developed on sticky surfaces, such as soda 
cans and candy wrappers. SPR reagent-developed latent prints can be lifted 
with clean lifting tape. 

Margot and Lennard found that the crystalline structure of the MoS, 
used in the recipe can have a significant effect on latent print development 
results. 9 They recommended using ROCOL™ AS powder, made up as 10 g 
with 0.8 mb Tergitol 7 in a 100-mL stock solution. This stock is then diluted 
1:10 for dipping and 1:7 for spraying. They further noted that substituting 
iron oxide as the powder component, as suggested by Haque et ah, 33 proved 
less effective in their experience than the molybdenum disulfide. 

Ishizawa and collaborators reported testing both white and black sus- 
pended particle mixtures in several “fixer” solutions. 34 The white particle 
mixture consisted of 80% agalmatolite, 10% lithopone, and 10% zinc oxide, 
all w/v in the fixer. Black particle mixture was 45% carbon black and 55% 




carbon graphite. The best “fixer” was a proprietary silicone-based, water- 
soluble coating named SP-F (Taiho Kogyo Co. Ltd.). Frank and Almog 35 
tested particles other than MoS 2 in suspension, including barium sulfate, 
titanium dioxide, talc, zinc oxide, zinc carbonate, and basic zinc carbonate 
to look for a suitable lighter colored entity to interact with the fingerprint 
residue. Best results were seen with 0.66 g zinc carbonate, 20 mL water, 0.06 
g Tergitol 7, and 55 g dimethyl ether. They further noted that particles of 
2-pm average size adhered better than those of 6-pm average size. Springer 
and Bergman 36 have described the preparation of SPR containing the fluo- 
rescent dyes Rhodamine 6G and Brilliant Yellow 40 (BY40). The basis for 
using these dyes is more fully developed below under post-treatment of 
cyanoacrylate latent prints. The preparations all worked initially, but the R6G 
reagent had poor shelf life. A BY40 suspension of 100 mL of 0.1% BY40 in 
ethanol mixed with 100 mL stock SPR showed consistently good results. 



Chemical Fuming and Enhancement 
Iodine Fuming 

The iodine fuming technique has been used for latent print development for 
at least a century. Several variations of the fuming procedure have been 
proposed over the years. 1,37 ' 39 The mechanism of the iodine fuming reaction 
was initially thought to involve the reversible addition of iodine to the double 
bonds of the unsaturated fatty acids in fingerprint residue by the process of 
halogenation. More recent research by Almog, Sasson, and Anah 40 suggests 
that the mechanism of interaction involves physical absorption rather than 
a chemical reaction. When iodine crystals are warmed, they produce a violet 
iodine vapor by sublimation. The iodine fumes are absorbed by the finger- 
print secretion residues to give yellowish brown latent prints. The iodine 
color is not stable, however, and is short-lived unless the iodine is chemically 
fixed (see below). There are four ways to develop latent prints with iodine. 

Iodine Fuming Gun Method 

An iodine fuming gun can be made from either a glass or hard plastic tube. 
Fresh calcium chloride crystals should be used as a drying agent. 

1. Place 0.5 g iodine crystals into the fuming gun. 

2. To fume a surface containing latent prints, the nozzle of the fuming 
gun is moved slowly over the surface at close range, approximately 
0.5 in. away. 

3. Blow air into the mouthpiece of the fuming gun (the end containing 
the calcium chloride crystals) through a connecting tube. 




4. Avoid inhaling any iodine fumes or allowing any contact of the vapors 
with skin. Iodine crystals and vapors are toxic and corrosive. 

5. Concentrate the fumes in areas where latent prints begin to appear. 

6. Photograph the developed fingerprint as soon as possible or, alterna- 
tively, fix the developed latent print with iodine fixing chemicals. 

Iodine Fuming Cabinet Method 

1. Suspend specimens or articles to be treated in the upper portion of 
the fuming cabinet. 

2. Place approximately 1 g iodine crystals in a clean evaporating dish in 
the cabinet. 

3. Close the fuming cabinet door. 

4. Heat the iodine crystals slowly and gently to about 50°C with a heating 
block or other appropriate heat source apparatus. 

5. Observe the development of latent prints. When maximum contrast 
has been achieved between the latent print and the background, 
remove the remaining iodine crystals from the cabinet. 

6. Remove the specimens from the cabinet. 

7. Photograph the developed fingerprint as soon as possible or, alterna- 
tively, fix the developed print with fixing chemicals. 

Iodine Dusting Method 

Iodine crystals are ground into a fine powder and dusted onto the surface 
containing latent fingerprints with a fingerprint brush in the same manner 
as that used with regular fingerprint powder. 

Iodine Solution Method 

Haque, Westland, and Kerr 41 reported that, by dissolving iodine in the 
7,8-benzoflavone fixation reagent, fingerprints that were several weeks old 
could be developed on various porous surfaces. Compared with the iodine 
fuming techniques, this technique showed improved convenience and sensi- 
tivity. Pounds and Hussain 42 have noted that a working solution consisting 
of 2 mL of 10% 7,8-benzoflavone in dichloromethane and 100 mL of 0.1% 
iodine in cyclohexane can be painted onto large surfaces at a crime scene to 
reveal latent prints. The technique was particularly effective in revealing 
freshly deposited latent fingerprints. The technique of adding the 7,8-ben- 
zoflavone to the iodine reagent for either spraying or solution application is 
described by Margot and Lennard as well. 9 

Although the iodine fuming technique is simple to use, it suffers from 
several disadvantages: the vapors are toxic and corrosive, iodine-developed 
latent fingerprint images fade away rapidly upon standing in air, and old 




latent prints are difficult to develop. Almog, Sasson, and Anah 40 reported a 
method in which controlling the addition of water vapor to the iodine fumes 
solved the problem of recovering aging latent prints. They showed that latent 
prints up to 110 days old could be developed on paper by this method. 

Methods exist for fixing iodine-developed fingerprints. These methods 
include starch spray, 43 silver plate transfer, 44 tetrabase solution, 45 and ben- 
zoflavone reagents. 41,46 The best results are usually produced by treating the 
iodine-developed fingerprint with 7,8-benzoflavone (a-naphthoflavone) 
reagent. The following is a commonly used formula: 

1. Dissolve 1 g a-naphthoflavone in 50 mL acetic acid. 

2. Add 300 mL 1,1,2-trichlorotrifluoroethane to the above solution. A 
clear, yellow iodine fixing solution is produced. 

3. Store the solution in a brown glass bottle; it will be stable indefinitely. 

Midkiff, Codell, and Chapman described an iodine fuming procedure fol- 
lowed by benzoflavone fixation that performed well on clear and light-col- 
ored tapes. 47 

Cyanoacrylate (Super Glue) Fuming 

In 1982, latent fingerprint examiners working at the U.S. Army Criminal 
Investigation Laboratory in Japan (USACIL-Pacific) and in the Bureau of 
Alcohol, Tobacco and Firearms (BATF) laboratory introduced a novel pro- 
cedure to the U.S. that used alkyl-2-cyanoacrylate ester (Super Glue) as a 
means of developing latent prints. The method was first devised by the 
Criminal Identification Division of the Japanese National Police Agency in 
1978. Since its introduction into the U.S., the method has received much 
attention from researchers who have evaluated it and attempted to improve 
its sensitivity and extend its range of application. 48 51 The principles under- 
lying the cyanoacrylate fuming method and its reaction have also been dis- 
cussed. 52 The structure of 2-cyanoacrylate ester and the mechanism of its 
polymerization are shown in Figure 4.1. 

Cyanoacrylate fuming has been successfully used for the development of 
latent prints on surfaces as diverse as plastics, electrical tape, garbage bags, 
Styrofoam, carbon paper, aluminum foil, finished and unfinished wood, 
rubber, copper and other metals, cellophane, rubber bands, and smooth 
rocks. The cyanoacrylate fuming procedure and several modifications of it 
that accelerate the development of latent prints are given below. 

Cyanoacrylate Fuming Procedure 

The equipment and materials required include cyanoacrylate and a fuming 
tank, cabinet, or other suitable container with a proper ventilation system. 



CN 



A- 



ch 2 =c— coor «I 



POLYMER 



Further 



Reaction 



CN 

CH 2 — C— COOR 

5 + 8- 



A- 



CN 

I 

A-CH 2 — C — COOR 

© 



CN 

I 

A-CH2 — C — CH2 — C — COOR 




COOR 



© 



Figure 4.1 Cyanoacrylate ester structure and polymerization mechanism. 



1 . Place the specimens or items on which latent prints are to be developed 
into the cabinet. They should be suspended from the upper portions 
of the cabinet if possible to allow their surfaces to be exposed to the 
cyanoacrylate fumes. 

2. Place 2 or 3 drops of liquid cyanoacrylate into a small porcelain dish, 
and place the dish into the fuming cabinet. 

3. Allow the items to be exposed to the fumes for at least 2 hr until 
whitish- colored fingerprint patterns appear. 

The cyanoacrylate-developed print may be further enhanced by dusting with 
regular or magnetic fingerprint powder. 

Fume Circulation Procedure 

In addition to the equipment required for the regular cyanoacrylate fuming 
procedure, the fume circulation technique requires a small battery-operated 
fan or air- circulating pump. 

1. Place the specimens and Super Glue in the porcelain dish into the 
cabinet as in the regular procedure. 

2. Turn on the fan. Its motion will circulate the fumes and increase the 
surface contact between latent print residues and cyanoacrylate 
vapors. Alternatively, a small circulating motor, such as a fish tank 
water pump, can be used to force the cyanoacrylate vapors to circulate 
in the fuming tank. 

3 . Allow the item to fume for 1 to 2 hr until a whitish-colored print appears. 

The developed prints may be enhanced by dusting as noted above or by other 
methods discussed below. 





Heat Acceleration Procedure 

In addition to the equipment required for the general procedure, the heat 
acceleration procedure requires a heating apparatus, such as a light bulb, 
portable heater, hot plate, hair dryer, or alcohol lamp. 

1. Place the specimens and Super Glue in the porcelain dish into the 
cabinet as in the regular procedure. 

2. Place the heating apparatus under the porcelain dish or arrange for 
the heat to contact the dish. The heat accelerates the polymerization 
process in the cyanoacrylate and increases monomer volatility, result- 
ing in faster vapor release and thus faster development of the latent 
print. 

3. Allow the item to fume for 20 to 40 min, until a whitish-colored print 
appears. 

The developed prints may be enhanced by dusting as noted above, or by 
other methods discussed below. 

Chemical Acceleration Procedure 

In addition to the equipment and reagents required for the general procedure, 
the chemical acceleration procedure requires 0.5 N sodium hydroxide and 
cotton pads or other absorbent media. 53 

1. Prepare 0.5 N sodium hydroxide by dissolving 2 g solid NaOH in 
1 00 mL distilled water. 

2. Place a clean cotton pad, cotton ball, or other absorbent medium into 
the dish. 

3. Place 2 or 3 drops of liquid cyanoacrylate onto the absorbent medium. 

4. Add 2 drops of 0.5 N sodium hydroxide solution to the absorbent 
medium. 

5. Allow the item to fume for 30 min to 1 hr until a whitish-colored 
print appears. 

The developed print may be enhanced by dusting as noted above, or by 
other procedures discussed below. 

Vacuum Acceleration Procedure 

Not long ago, a new vacuum acceleration technique was developed by Watkin 
of the Royal Canadian Mounted Police (RCMP) Identification Division. 54,55 
It was found that cyanoacrylate is easier to vaporize and the vapor is more 
effective using this procedure. In a limited comparison study, a majority of 
latent examiners preferred prints developed by the vacuum procedure. 56 




Large vacuum chambers for processing a variety of objects are available 
commercially. Margot and Lennard 9 generally agree on the usefulness of this 
procedure. 

Other Acceleration Procedures 

Many other acceleration procedures have been used, including heating com- 
bined with circulation, intense heating combined with the addition of poly- 
merization retardant to the cyanoacrylate, moist vapor combined with 
heating, cyanoacrylate in gel media, and combinations of chemical acceler- 
ators. All these techniques have the same two basic objectives: (1) accelerate 
the polymerization process and (2) prolong the volatilization. Grady 57 
described good results from a combination of heating within a vacuum 
chamber. He noted that although development could not be monitored, 
overfuming was rare and that background dye stain fluorescence was reduced. 

Cyanoacrylate ester has been incorporated into a gel matrix that is placed 
in a foil pouch that is reusable and has wide applications for processing latent 
prints. In 1985, Gilman, Sahs, and Gorajczyk 58 also reported a similar method 
in which a mixture of cyanoacrylate and petroleum jelly are sandwiched 
between acetate sheets. It has also been found that cyanoacrylate fuming is 
an excellent method for processing latent prints in motor vehicles and in 
small enclosed spaces at crime scenes. Olenik 59 has described another sand- 
wich technique in which a thin film of cyanoacrylate is placed between 
aluminum foils by the use of a fingerprint roller. 

Even when care is exercised, fingerprints can be overdeveloped with 
cyanoacrylate. Springer 60 noted that carefully controlled heating of the over- 
developed print at 70 to 80°C can selectively remove enough cyanoacrylate 
polymer to render the print identifiable. However, one cannot re-fume the 
latent after this procedure has been used. The technique was based on the 
observation by Almog and Gabay, 61 later confirmed by Davis, McCloud, and 
Bonebrake, 62 that polymerized (solidified) Super Glue produces fumes, i.e., 
monomeric vapor, upon heating. Geng described several methods of apply- 
ing organic solvent mixtures (such as spraying, dipping, etc.) to overdevel- 
oped Super Glue prints to render them more suitable. 63 The composition of 
the treating solvent and method of application depended on the surface. 

Though not an “acceleration” procedure, Zhang and Gong 64 described a 
cyanoacrylate ester dry transfer method that placed test objects in contact 
with neutral filter paper that had been pre-treated with Super Glue, then 
dried. Additionally, various applications to special situations or conditions, 
such as large or immovable objects, plastic bags, leaves, surfaces contami- 
nated by cigarette smoke residues, etc., have been noted periodically. 65-70 




Further Enhancement and Post-Treatment Procedures after 
Cyanoacrylate Processing 

Although cyanoacrylate fuming is an excellent method for processing, the 
latent prints developed by this procedure often lack contrast and are difficult 
to visualize. Over the years, several methods for enhancing cyanoacrylate- 
developed prints have been reported. The most common one is simply to 
dust the developed print with fingerprint powder. In addition, cyanoacrylate- 
developed latent prints may be further enhanced by staining with any of 
several histological dyes in solution, mixtures of them, or other compounds 
that luminesce or fluoresce under UV, laser, or other illumination. Treatment 
with visible or luminescence-inducing dyes is commonly called “dye stain- 
ing.” These post-treatments are particularly useful on multicolored or other 
surfaces that do not contrast well with directly developed cyanoacrylate 
prints, and that are not highly luminescent themselves. Either gentian violet 
or coumarin 540 laser dye, 71 staining with Ardrox dye and examining with a 
UV light source, 9,72 " 74 by staining with Rhodamine 6G and examining with a 
laser, 75 by dusting with fluorescent powder, 76 and by combining acrylate 
fuming with the ninhydrin/zinc chloride method with laser examination 77 
have all been described. Weaver and Clary 78 described a one-step procedure 
using the Super Glue “fuming wand” with various cyanoacrylates into which 
had been incorporated several proprietary fluorescent dyes, followed by 
examination with the argon laser. Some of the reagents and procedures are 
given below. 

Gentian Violet Solution — Phenol Containing Formulation. 

Stock solution 

Gentian violet 5 g 

Phenol 10 g 

Ethanol 50 mb 

Working solution 

Stock solution is diluted to 150 mL with water. 

Cyanoacrylate-developed prints are immersed in the working gentian violet 
solution for about 1 min with gentle rocking. The article bearing the latent 
print is then removed and excess dye is removed with running water. For 
larger articles, a pipette or syringe can be used to cover the developed print 
areas with an excess of the reagent. 




Gentian Violet Solution — Non-Phenol Formulation. Phenol is very caus- 
tic, and correspondingly hazardous. The FBI Laboratory procedures 79 and 
those of some other U.S. laboratories 80 call for preparing the solution by 
dissolving 1 g dye in 1 L distilled water. The item is treated by dipping or 
painting for 1 to 2 min and then rinsed off under cold water. The solution 
has a long shelf life when stored in a dark bottle. 

There is some indication 81 that the phenol-containing formulation may 
perform better than the strictly aqueous solution. Margot and Lennard 9 
describe a solution made from 0.1 g dye in 10 mL acetonitrole and 5mL 
methanol and brought to 100 mL with “Arklone” (trichlorotrifluoroethane). 
Bramble et al. 82 recently reported optimizing the absorption and emission 
wavelengths for latent viewing after gentian violet development. It may also 
be noted that gentian violet processing has been commonly used for pro- 
cessing sticky tape surfaces (see below) and for more common surfaces with 
no preceding cyanoacrylate treatment. 83 

Coumarin 540 Dye Staining Method. The reagent is made by dissolving 

0.01 g coumarin 540 in 150 mL ethanol. The item can be immersed in the 
solution, or the solution can be applied to the latent print areas with a suitable 
device as in the gentian violet procedure above. Excess reagent is removed 
by overlaying the treated area with absorbent paper or similar material. 

Ardrox Dye Staining Method. In 1986 Vachon and Sorel 73 first reported 
the Ardrox dye staining technique. Ardrox is an industrial dye manufactured 
in Canada, and it is reported to be noncarcinogenic and nonhazardous; 
however, it may dry the skin. Miles reported an improved-staining Ardrox 
solution using 1,1,2-trichlorofluoroethane (Freon 113) as the main carrier. 72 
McCarthy 74 has suggested the following modified procedure: 

1. Mix 1 mL of Ardrox P133D in 60 ml of methanol. 

2. Mix the Ardrox-methanol solution with 40 ml of Freon. 

3. Immerse the object into the solution for 1 min. 

4. Rinse the object with tap water and air dry. 

5. Examine the object under a UV light source. 

Margot and Lennard 9 use 1 mL Ardrox 970-P10 in 8 mL methyl ethyl 
ketone and bring this up to a final volume of 100 mL with petroleum ether. 
Another variation consists of 1 mL Ardrox in 9 mL isopropanol and 15 mL 
methyl ethyl ketone (MEK) to which is added 75 mL distilled water. 84 The 
more recent formulations represent attempts to find substitutes for the now 
banned Freon solvents (see further below). 




Other Dyes and Dye Mixtures. Several other dyes have been used for the 
post-treatment of cyanoacrylate-developed fingerprints. These include 
Rhodamine 6G (R6G), basic yellow 40 (BY40), basic red 28 (BR28), and 
styryl 7 (S7). Mazzella and Leonard 85 looked at Rhodamine 6G, basic yellow 
40, basic red 28 and styryl 7 separately and in various combinations. For- 
mulations were: for R6G, 20 mg R6G in 60 mL propanol and 40 mL aceto- 
nitrile stock, and 5 mL of this stock to 100 mL petroleum ether for working 
solution; for BY40, 100 mg in 60 mL propanol and 40 mL acetonitrile stock, 
and 5 mL of this stock to 100 mL petroleum ether for working solution; for 
BR28, 200 mg BR28 in 60 mL propanol and 40 mL acetonitrile stock, and 
5 mL of this stock to 100 mL petroleum ether for working solution; and for 
styryl 7, 100 mg styryl 7 as for the others. Dye mixtures were prepared as: 
for BY40 + BR28, 3 mL BY40 stock and 2 mL BR28 stock in final volume of 
100 mL petroleum ether; for BR28 + S7, 3 mL BR28 stock and 2 mL S7 stock 
in final volume of 100 mL petroleum ether; and for BY40 + BR28 + S7, 2 mL 
BY40 stock + 2 mL BR28 stock and 2 mL S7 stock to a final volume of 100 mL 
with petroleum ether. These formulations appear in Margot and Lennard 9 
as well. BR28 was an excellent enhancement dye. S7 was found not to be 
especially stable. Olenik 86 described a simple three-dye blend consisting of 
Ardrox P133D, R6G, and BY40: 1 L of the solution was made by adding 1 g 
BY40, 0. 1 g R6G, and 8 mL Ardrox to 940 mL isopropanol or denatured ethanol. 
Adding an additional 50 mL acetonitrile enhanced the luminescence effects. 

Various different dyes are used to post-treat cyanoacrylate-developed prints 
because they have different absorption and emission maxima and thus offer 
versatility in enhancing latent fingerprints on various types of surfaces that can 
themselves be multicolored and have varying luminescence characteristics. Dye 
mixtures increase versatility through intermolecular energy transfers that enable 
the examiner to take advantage of one dye’s absorption maximum while mon- 
itoring luminescence at another dye’s emission wavelength. 

Cummings, Hollars, and Trozzi 87 did similar studies on a number of dye 
mixtures for the treatment of cyanoacrylate-developed latents. Some of their 
stock and working solution recipes differ slightly from those above. Two 
mixtures are of interest. So-called RAM is Rhodamine 6G, Ardrox, and MBD. 
MBD is 7-(p-methoxybenzylamino)-4-nitrobenz-2-oxa-l, 3-diazole. Stock 
solutions are 

R6G: 100 mg in 100 mL methanol 

MBD: 100 mg in 100 mL acetone 

RAM is then made using 3 mL R6G stock, 2 mL Ardrox P133D, and 7 mL 
MBD stock in 20 mL methanol, 10 mL isopropanol, 8 mL acetonitrile, and 




Table 4.1 Approximate Absorption and Emission 
Maxima of Dyes and Dye Mixtures Used to Visualize 
Cyanoacrylate-Developed Latent Prints 



Dye/Dye Mixture 


Absorption Max 
(nm) 


Emission Max 
(nm) 


Rhodamine 6G 


525 


555 


Ardrox 


380 


500 


MBD 


465 


515 


RAM 


460 


555 


Basic Yellow 40 (BY40) 


440 


490 


Basic Red 28 (BR28) 


495 


585 


Styryl 7 (S7) 


555 


680 


BY40 + BR28 


445 


590 


BR28 + S7 


510 


680 


BY40 + BR28 + S7 


445 


680 



950 mL petroleum ether (in order). A “modified” RAM consisted of 30 mg 
MBD, 25 mL acetone, 40 mL ethanol, 15 mL 2-propanol, and 950 mL petro- 
leum ether, 1 mL Ardrox P133D, 5 mL R6G stock, and 20 mL acetonitrile 
(combined in order). 

A second mixture formulation, called “MRM 10,” requires another dye, 
Yellow 40 (Maxilon Flavine 10GFF). The Yellow 40 (Y40) stock is 2 g Yellow 
40 on 1 L methanol. MRM 10 is then 3 mL R6G stock, 3 mL Y40 stock, 7 mL 
MBD stock, 20 mL methanol, 10 mL 2-propanol, 8 mL acetonitrile, and 
950 mL petroleum ether (combined in order). 

Morimoto, Kaminogo, and Hirano subjected cyanoacrylate-developed 
prints to sublimates of l-amino-2-phenoxy-4-hydroxy-anthraquinone and 
l,4-bis(ethylamino)-anthroquinone. 88 Sublimation was achieved by incorpo- 
rating the dyes into incense sticks. Kempton and Rowe 89 dye-stained 
cyanoacrylate-developed prints with several histological stains as well as with 
commercial “Rit” dyes. Generally, methanolic solutions were superior to 
aqueous ones on most tested surfaces. Prints treated with gentian violet, 
diamond fuchsin, and “safranin bluish” fluoresced under 312 nm light (saf- 
ranin the strongest). Day and Bowker 90 reported good results with Nile Red 
as a post-cyanoarylate dye stain. Table 4.1, modified from Margot and Len- 
nard, 9 shows absorption and emission maxima and is helpful in understand- 
ing the reasons for choosing these various cyanoacrylate-developed print 
post-treatment dyes and dye mixtures. 

Rare Earth Complexes. Wilkinson and Watkin reported good results in 
enhancing cyanoacrylate-developed prints with a aryl diketone chelate of 
europium (Eu), called TEC. 91 The idea for this enhancement technique was 
based on the fact that rare earths like europium have narrow emission bands 



and long excited state lifetimes (see below for further development of the 
origins of using rare earth complexes). However, Eu is a poor light absorber, 
so the organic ligand functions as an efficient absorber and intramolecular 
energy transfer entity, resulting in characteristic Eu fluorescence at 615 nm. 
The reasoning behind the method is similar to that underlying the metal ion 
enhancement of ninydrin-developed latent prints. 

Lock et al. tested several Eu complexes and reported good results after 
treating cyanoacrylate-developed prints with europium thenoyltrifluoroace- 
tone ortho-phenanthroline (EuTTAPhen). 92 The stock solution was 0.5 g 
EuTTAPhen in 60 mL propanol and 40 mL acetonitrile. A working solution 
was made by diluting 5 mL of this stock to 100 mL final with petroleum ether. 
Effectiveness was assessed by comparison with TEC. Generally, the formula- 
tion was said to behave similarly to TEC, but gave better luminescence yields. 

Fluorescent and Other Chemical Fuming/Treatment Procedures 

Some fluorescent reagents have low sublimation temperatures, i.e., as with 
iodine, these chemicals will vaporize appreciably at temperatures below their 
melting point. The fluorescent reagent vapors can thus be used for developing 
and visualizing latent fingerprints in a manner similar to that of iodine 
fuming. Almog and Gabay 61 tested eight fluorescent chemicals (anthracene, 
anthranilic acid, perylene, Rhodamine B, Rhodamine 6G, 7-diethylamino- 
4-methylcoumarin, triphenylcarbinol, and antimony trichloride) that sub- 
lime readily. They found that all eight chemicals produced clear impressions 
of the latent prints under UV light. The best results for fresh fingerprints 
were obtained with anthranilic acid. For older prints, anthracene produced 
somewhat better results. The results with Rhodamine B and Rhodamine 6G 
were less satisfactory. 

Other fluorescent chemicals such as 8-hydroxyquinoline and dimethox- 
ycoumarin have also been reported to be useful fuming reagents for latent 
fingerprint detection (Forensic Science Institute, People’s Republic of China, 
personal communication, 1989.). 8-Hydroxyquinoline has been used as a 
field fuming reagent in searching for latent prints at crime scenes. 

The fumes of many other materials, such as camphor, pine tar, nitrocel- 
lulose, magnesium, and titanium tetrachloride, can be generated by heating 
the materials and used for the detection of latent fingerprints. 1,93,94 However, 
the means by which the fumes are formed is different from that of iodine 
fuming, and most of these fuming techniques have only historical interest. 
Radioactive sulfur dioxide gas fuming has also been reported to be a useful 
technique for the detection of latent fingerprints on a variety of surfaces, 
including paper, adhesive tapes, and fine fabrics. 95 After an exhibit has been 
exposed to radioactive 35 S0 2 , the presence of fingerprints may be detected 




and recorded by autoradiography. Nitric acid fumes have been used for the 
detection and visualization of latent fingerprints on brass casings and metal 
objects under special conditions. 96 

Sodhi and Kaur 97 reported good results in the detection of latent prints 
with eosin blue dye in the presence of f-tetrabutyl ammonium iodide, 
referred to as a “phase transfer catalyst.” No illumination or luminescence 
techniques were used. 

It has been clear for a long time that dimethylaminocinnamaldehyde 
(DMAC), which reacts with urea, a component of eccrine sweat and thus of 
eccrine fingerprint residue, can be used to enhance latent prints. 6,98 Finger- 
print examiners have long assumed that the DMAC reacts exclusively with 
urea in latent residue because of its established reaction with urea. For exam- 
ple, DMAC has been used for years by biological evidence analysts as the 
basis for a presumptive test for urine. DMAC can also react with primary 
and secondary amines, and the basis for its reaction with latent residue has 
recently been questioned. 99 An earlier common formulation used a 35% 
ethanol, 65% Freon solvent. Ramotowski" noted that the following formu- 
lation gave good results: 

Solution A 

DMAC 0.25 g 

Ethanol 50 mL 

Solution B 

Sulfosalicylic acid 1 g 

Ethanol 50 mL 

Solutions A and B are mixed together in equal proportions just before 
use. Solution A may require a quick filtration to remove particulates prior 
to mixing it with Solution B. Margot and Lennard noted that the reaction 
product is unstable and that DMAC-developed prints should be photo- 
graphed immediately. 9 Sasson and Almog also noted some of the limitations 
of this reagent. 98 More recently, Brennan et al. reported fairly good results 
with a DMAC fuming technique. 100 DMAC did not interfere with the subse- 
quent use of DFO or PD on paper substrata, but was not compatible with 
cyanoacrylate processing. It was said to give good fluorescent results with 
latents on fax-type papers. Both Menzel 20 and Katzung 101 previously 
described the luminescent properties of the DMAC-urea complex, and the 
best results from this study took advantage of luminescence using narrow- 
band illumination. Ramotowski" said that use of a vapor contact procedure 
significantly reduced background fluorescence. 




A method involving immersion or spraying with ruthenium tetroxide 
(RTX) was described by Mashito and Miyamoto. 102 It has been noted that 
RTX may be exceptionally toxic. 103 

Wilkinson described a Eu-(TTA)3-2TOPO chelate formulation for latent 
fingerprints with significant lipid content. 104 This procedure was based on 
the principles discussed above as the basis of TEC processing of cyanoacry- 
late-developed latents. 

A method based on similar principles but arrived at independently was 
described by Allred and Menzel. 105 They used 1,10-phenanthroline and the- 
onyltrifluoroacetone as secondary complexing agents for the Eu ion after an 
EDTA-Eu ion chelate had reacted with the lipid residues in the latent residue. 

Murphy et al. 106 described a newly synthesized porphyrin derivative 
whose chemical properties would suggest it might be suitable for reac- 
tion/interaction with either lipid or water-soluble components of latent print 
residue. Formulations of the compound were compared with PD and with 
ninhydrin and DFO in test latents. DFO generally performed better with 
fresher prints but the converse was true with older ones. With latents on 
thermal fax paper, the compound performed better than ninhydrin or DFO. 



Ninhydrin and Chemical Alternatives 
Ninhydrin 

As early as 1910, Ruhemann in England and Abderhalden and Schmidt in 
Germany reported that alpha amino acids, polypeptides, and proteins formed 
color products upon reaction with ninhydrin. In 1954, the Swedish scientists 
Oden and von Hofsten advocated the use of ninhydrin for developing latent 
fingerprints. 107 In 1955, Oden patented the process as a latent fingerprint 
techinque. Various concentrations of the ninhydrin solution have been sug- 
gested, the concentration of ninhydrin varying from 0.2 to 1.5%. 39,108 " 110 
Various types of solvents, such as acetone, methanol, ethanol, ethyl ether, 
ethylene glycol, petroleum ether, naphtha, Freon 113 (trichlorotrifluoro- 
ethane), and combinations of solvents, 111 115 have been used for ninhydrin. 
Although differences still exist over the optimal concentration of ninhydrin 
and the ideal solvent, the best results may ordinarily be obtained with con- 
centrations ranging from 0.6 to 1.0% in Freon 113. The selection of the 
appropriate concentration and solvent for latent fingerprint detection 
depends on the type of material being processed and whether or not there 
is any writing on the material. The so-called NFN (nontoxic, nonflammable) 
formulation that is made up in Freon, as well as its variations which have 
been widely used, originated with Morris and Goode. 115 




Ninhydrin solutions may be applied by spraying, swabbing, or dipping. 
Post-processing treatment by the application of heat can be used to accelerate 
the reaction. Various temperatures and equipment (such as ovens, irons, 
steam irons, hair dryers, or microwave ovens) have been suggested for post- 
processing heating. Optimal results have been obtained when ninhydrin- 
treated documents were heated to 80°F in 80% relative humidity. 1 The fol- 
lowing recipes are CFC free (see below) and represent recent efforts to refor- 
mulate a number of fingerprint reagents because of the probable 
unavailability of the chlorofluorocarbon (CFC) solvents. The original nin- 
hydrin formulation involved making 15 g up in 30 mL glacial acetic acid and 
60 mL absolute ethanol, then diluting 3 mL of this stock with 100 mL fluo- 
risol. 

Reagents 

According to Watling and Smith: 116 

1. Prepare a stock ninhydrin solution with either: 



Ninhydrin 33 g 

Absolute anhydrous ethanol 225 mL 

or 

Ninhydrin 30 g 

Absolute anhydrous ethanol 225 mL 



2. Remove 400 mL heptane from a 4-L bottle and reserve. 

3. Add the ninhydrin-ethanol solution to the bottle; shake vigorously; 
top off with the reserved heptane. 

Note: Crystals may form in the alcohol solution, that may be helped into solution by 

gentle warming. 

According to Hewlett, Sears, and Suzuki: 117 



Ninhydrin 


5 g 


Absolute anhydrous ethanol 


75 mL 


Ethyl acetate 


25 mL 


Glacial acetic acid 


3 mL 


Heptane 


1 L 



Another recipe for ninhydrin spray solution consists of 25 g ninhydrin in 4 
L acetone, stirred well and stored in a dark bottle. 




Procedure 



1. Fill the spray unit with the working ninhydrin solution and spray the 
surface containing the latent print from a distance of about 6 in. 

2. Allow the solvent to evaporate and then repeat the spraying process. 

3. After spraying, the surface can be heated with an infrared lamp or 
steam iron for a short period. Be careful not to overheat the surface 
and do not allow the heat source to come into direct contact with the 
surface. 

4. Alternatively, leave the specimen at room temperature until the latent 
print fully develops. It may take quite a bit longer to develop prints 
at room temperature than it would if the development is heat 
enhanced. However, it often yields more satisfactory results. 

As just noted in connection with the ninhydrin solution formulation, a 
number of latent print investigators have recently focused attention on refor- 
mulating ninhydrin, its analogues, and other chemicals that are commonly 
sprayed (such as DFO) in solvents/vehicles other than Freon 113. Freon 113 
(CFC 113, 1,1,2-trichlorotrifluoroethane) was included in the “Montreal Pro- 
tocol” signed in 1987 which banned CFCs in most of the industrialized 
countries because of concerns about the ozone layer. It appears likely that 
CFCs will not be available for this purpose. It should be noted that Watling 
and Smith 116 and Hewlett, Sears, and Suzuki 117 used heptane as the solvent 
because of the resulting reagent’s performance; heptane is extremely flam- 
mable. Margot and Lennard 9 noted that they have substituted mainly petro- 
leum ether, even though care and attention are necessary because of the 
potential fire hazard. Jungbluth 118 explored an industrial solvent called Gene- 
solv 2000 for both ninhydrin and DFO and found it to be satisfactory, and 
Hewlett et al. 117 ’ 119 found the hydrofluorocarbons (HFCs) HFC4310mee and 
HFE7100 to be promising ninhydrin solvents, but not as good overall as the 
heptane based formulation. 

Marquez described a modified ninhydrin development procedure appli- 
cable to carbonless form documents. 120 Here, the ninhydrin solution was 
prepared in ethanol and heptane. Filter paper pieces the size of the document 
were saturated with the ninhydrin solution and then allowed to dry. The 
document was then sandwiched between the filter papers and heat applied 
for 30 min, after which the document was placed in a humid chamber. This 
method was said to prevent the ninhydrin solvent from causing running of 
the writing on the carbonless document. Pressly described the successful 
processing of latent prints on latex gloves using a ninhydrin dipping proce- 
dure, but with no heating. 121 Margot and Tennard said that heat acceleration 




of development of ninhydrin-treated latent prints should be avoided, but 
especially avoided if any post-treatment with metal salts is to be effective. 9 



Pre-Treatment and Post-Treatment Techniques for the 
Enhancement of Ninhydrin-Developed Latent Prints 

Ninhydrin-developed fingerprints often lack contrast because of the color of 
the background surface. In 1981, German 122 reported the utilization of lasers 
to examine ninhydrin-treated latent prints. Kobus, Stoilovic, and Warrener 123 
described a simple post-ninhydrin treatment technique using zinc chloride 
and xenon arc light to yield luminescent latent print images. They found that 
this method improved the visualization of latent prints on paper where 
ninhydrin alone gave poor results. 

Herod and Menzel found that latent prints that did not develop well with 
ninhydrin could be brought out if examined under dye laser light. 124 Subse- 
quently, they suggested two modified treatments for using ninhydrin to 
develop latent fingerprints: 77,125 pre-treatment with trypsin and post-treatment 
with metal salts. In the first modification, latent prints were treated either by 
spraying with a methanol solution containing both ninhydrin and trypsin 
or by spraying first with a water solution of trypsin and then with ninhydrin 
under room light. The samples sprayed first with trypsin and then with 
ninhydrin showed a somewhat better development than those treated either 
by the combined solution or by ninhydrin alone. Results under dye laser 
examination showed no dramatic improvement. In the second modification, 
ninhydrin-developed latent prints were sprayed with solutions of nickel 
nitrate, zinc chloride, and cadmium nitrate and then examined by argon laser 
light. It was found that a combination of the ninhydrin-zinc chloride proce- 
dure and 488-nm argon laser light yielded the most promising results by far. 

Stoilovic et al. reported a method for improving the enhancement of 
ninhydrin-developed fingerprints by cadmium complexation using a low- 
temperature photoluminescence technique. 126 Everse and Menzel further 
reported that there was a pronounced enhancement of the detectability of 
latent prints by combining pretreatment with trypsin or pronase with post- 
treatment with zinc chloride followed by examination by argon laser light. 127 

Recently, researchers in Australia have found that metal complexes 
formed by using group lib transition metals show favorable luminescent 
properties at low temperatures (77°K) and that ninhydrin-treated fingerprints 
can be enhanced considerably. 128 The structure of the metal complexes formed 
between Ruhemann’s purple and group lib metal salts was also studied. 

Goode and Morris 6 reported that treating ninhydrin-developed finger- 
prints with metal solutions improves the contrast between the background 
and the print. Treatment with zinc chloride solution changes the purple color 




to orange. Treatment with nickel chloride solution produces an orange-red 
color. 

Use of metal ions to form luminescent complexes with the Ruhemann’s 
purple (RP) formed by the reaction of amino acids in the fingerprint residue 
and ninhydrin (or its analogues) has become a routine practice in developing 
latents on porous surfaces. Understanding the rather complicated chemistry 
underlying formation of these complexes also laid the groundwork for more 
recent work on the use of rare earth ions to induce luminescence 129,130 (and 
see below). This material has also been reviewed by Menzel. 20,131 Liberti, 
Calabro, and Chiarotti 132 have studied the stability of the zinc RP complexes. 

Ninhydrin/Zinc Chloride Procedures Without Freon : 118 

Ninhydrin solution 





Ninhydrin 


6 g 




Glacial acetic acid 


10 mL 




Methanol 


20 mL 


Note: 


Stir the above until completely dissolved, then: 




Genesolv 2020 


100 mL 


Zinc chloride solution 






Zinc chloride 


6 g 




Glacial acetic acid 


10 mL 




Ethanol 


50 mL 




Propanol 


10 mL 


Note: 


Stir the above until completely dissolved, then: 




Genesolv 2020 


200 mL 



Notes: Fingerprints developed first with cyanoacrylate are immersed in the ninhydrin 
solution, air dried, and then treated with the zinc chloride solution. The Super 
Glue treatment stabilizes inks on paper substrata so that they do not run when 
treated with the ninhydrin. 

Chemical Alternatives to Ninhydrin 

Ninhydrin has traditionally been the most common reagent employed for pro- 
cessing latent prints on paper. There are, however, several limitations to the 
ninhydrin method, such as the sensitivity of the ninhydrin reaction, background 
colors of the matrix surface, background coloration after ninhydrin treatment, 




and certain nonreactive surface materials. Numerous compounds have been 
reported as potential substitutes for ninhydrin in the detection of latent 
fingerprints. They can be divided into two categories: reagents for amino 
acid detection and ninhydrin analogues. This area has been thoroughly 
reviewed by Almog 133 and is the subject of Chapter 5 of this volume. 

Reagents for Detection of Amino Acids 

In the 1970s and 1980s, fluorescamine, 134 o-phthalaldehyde 135 and NBD- 
chloride (7-chloro-4-nitrobenzo-2-oxa- 1,3-diazole), 136,137 NBD -fluoride 
(7-fluoro-4-nitrobenzo-2-oxa-l, 3-diazole) (Criminal Investigation Bureau, 
Taiwan, Republic of China, personal communication, 1989), and dansyl 
chloride 138 had been suggested as substitute reagents for ninhydrin. These 
reagents react with amino acids in the fingerprint residues to produce fluo- 
rescent products that render the latent print pattern visible. 139 Studies have 
shown that these reagents not only have a greater sensitivity than ninhydrin 
but also work well for the detection of latent fingerprints on multicolored 
materials. An additional advantage of the treatment of latent prints with 
fluorescamine, o-phthalaldehyde and NBD-chloride (NBD-C1) is that they 
can subsequently be further enhanced with laser light, xenon arc light, or 
other light sources. 140 The principal disadvantages of these fluorigenic 
reagents are that they are not too stable in solution and sometimes produce 
interfering background luminescence. The procedures for preparing these 
reagents are as follows: 

Fluorescamine reagent 

Fluorescamine 20 mg 

Acetone 100 mb 

20% triethylamine-methylene chloride solution 4 mb 

Note: Fluorescamine is dissolved in acetone, the 20% triethylamine-methylene chlo- 
ride solution is added, and the pH is then adjusted to 9 to 11. 

o-Phthalaldehyde reagent 



Boric acid 


2.5 g 


Water 


95 mb 


4 N KOH 


See below 


30% Brij 35 solution 


0.3 mb 


2 -Mercaptoethanol 


0.2 mb 


o - Phthalaldehyde 


0.5 g 


Methanol 


1 mb 




Notes: Boric acid is dissolved in the distilled water, and the pH is adjusted to 10.4 with 
4 N KOH. This solution is then stabilized with the addition of the Brij 35 
solution and then reduced with the addition of 2-mercaptoethanol. The 
o-phthalaldehyde dissolved in the methanol is added last. 

Formulations available for the NBD-chloride, NDB-F, and dansyl chlo- 
ride reagents were provided in the previous edition of the chapter, but all of 
them are based on Freon. We are not aware of any substitute, CFC-free recipes 
that have been tested or validated for the development of latents. 

Almog et al. 141 have reported on a new series of fluorigenic reagents. Five 
nitrobenzofurazanyl ethers, 4-methoxy-7-nitrobenzofurazan (NBD-OCH 3 ), 
4-ethoxy-7-nitrobenzofurazan (NBD-OCH 2 CH 3 ), 4-(2-hydroxy)-7-nitroben- 
zofurazan (NBD-OCH 2 CH 2 OH), 4-(methoxy-ethoxy)-7-nitrobenzofurazan 
(NBD-OCH 2 CH 2 OCH 3 ), and 4-phenoxy-7-nitrobenzofurazan (NBD-OC 6 H 5 ), 
have been prepared and examined as potential reagents for the detection of 
latent fingerprints on paper. It was found that all five reagents developed latent 
prints with high sensitivity, similar to that of the parent compound NBD-C1. 
These reagents can also be used in vapor phase development. The study indicates 
that vapor phase development techniques have advantages, such as the avoid- 
ance of the use of solvents and the reduction of the background fluorescence 
and discoloration. Pounds 5,142 has reported on the use of l,8-diazafluoren-9-one 
(DFO) for the fluorescent detection of latent prints on paper. He found that 
fingerprints visualized by DFO revealed more ridge detail than those developed 
with ninhydrin/ZnCl 2 . DFO treatment can be used in conjunction with ninhy- 
drin, but must precede it. DFO treated paper substrata, subsequently developed 
with ninhydrin, yielded more prints than those developed with ninhydrin 
alone. 119 

The original preparation of DFO reagent used fluorisol. Other solvent 
systems besides methanol-fluorisol have been reported by Masters, Morgan, 
and Shepp (personal communication, 1990) and by Peigare (FBI, personal 
communication, 1990). The following is the formulation used by them. 



DFO stock solution 

DFO 1 g 

Methanol 180 mL 

Acetic acid 20 mL 

Working solution 

DFO stock solution 60 mL 

Acetone 50 mL 

2-Propanol 10 mL 




Procedure 



Xylene 

Petroleum ether 



50 mL 
830 mL 



1. Dip the paper containing latent prints into the freshly prepared solu- 
tion for 5 sec. 

2. Allow the paper specimen to dry for 30 sec. 

3. Repeat the dipping for another 5 sec (some indicate this step can be 
omitted) 

4. Heat the paper to 100°C for 10 min. 

5. View the surface under alternative light sources as follows: 

a. Video spectral comparator (VSC-1) using blue-green light 
excitation — Fluorescence can be observed through a 610-nm filter. 

b. A 12-W argon laser operated at 514 nm — Fluorescence can be 
observed through a 550- or a 610-nm filter. 

c. A mercury vapor lamp — Fluorescence can be observed through a 
546-nm filter. 

As noted above, Jungbluth 118 formulated DFO in a Freon substitute: 50 mg 
DFO is dissolved in 4 mL methanol and 2 mL acetic acid; then 94 mL Gene- 
solv 2000 is added. Geide 143 similarly formulated DFO in the Freon-substitute 
solvent t-butyl-methyl ether. He noted that the solvent is highly flammable 
and volatile and must be used with care in a hood. Bratton and Juhala 144 
described a sandwiching procedure in which the test item was sandwiched 
between DFO-treated filter papers and then subjected to 5% acetic acid 
“steam” (from a steam iron), to get around the problem of solvent-caused 
ink bleed on documents. 

Ninhydrin Analogues 

Almog, Hirschfeld, and Klug 145 synthesized several ninhydrin analogues: 
benzo [ e ] ninhydrin (2,2-dihydroxybenz [ e ] -indane- 1,3-dione), benzo [/] nin- 
hydrin (2,2-dihydroxybenz[/] -indane-l,3-dione), and 2,2-dihydroxy- 
5-chloro-6-methoxyindane-l,3-dione. These compounds were tested for 
their applicability to latent print detection. It was found that the ninhydrin 
analogues developed latent prints with a sensitivity similar to that of ninhy- 
drin and that the quality of development was independent of the age of the 
latent fingerprints. Benzo [f ] ninhydrin performance in several solvent formu- 
lations was recently compared directly with ninhydrin, and found to be 
superior for certain surfaces, but not in the number of prints developed on 
actual exhibits overall. 146 




More recently, Almog et al. have synthesized and evaluated a series of 
both 4- and 5-aminoninhydrins. 147 Absorption and emission characteristics 
of the compounds were determined and part of the evaluation was based on 
the reaction of the compounds with alanine in solution. The 5-aminoninhy- 
drins were superior to the 4-amino compounds. However, the 5-amino com- 
pounds gave significantly slower development than either ninhydrin or 
5-methoxyninhydrin. It was noted that the 5-amino compounds might prove 
useful as direct fluorigenic reagents for developing latent prints on fluorescent 
surfaces that absorb in the 400- to 500-nm range and emit at 550 to 650 nm, 
precluding the use of ninhydrin or 5-methoxyninhydrin. 

Menzel and Almog have studied the fluorescent properties of the finger- 
prints developed by ninhydrin analogues when complexed with zinc chloride. 
They found that only benzo[/] ninhydrin complex fluoresced as intensely as 
the ninhydrin complex, and its absorption maximum is 530 nm. The neody- 
miurmyttrium aluminum garnet (Nd:YAG) laser emits light at 532 nm and 
is more effective than the argon ion laser, which has emission maxima at 
488 nm or 514 nm. 148 

Lennard et al. 149 have synthesized methoxy, chloro, bromo, and perinaph- 
tho derivatives of ninhydrin. They found that fingerprints developed by all 
of the derivatives have the same sensitivity as ninhydrin and photolumines- 
cent complexes that were formed on addition of zinc and cadmium salts. 

Almog et al. 150 synthesized 5-methylthio-ninhydrin derivatives and tested 
them next to other ninhydrin analogues and DFO. They showed superior 
luminescence properties when the reaction product was complexed with zinc. 
Cantu et al. 151 compared a series of ninhydrin analogues using a dried amino 
acid spot model and found thienof/] ninhydrin to be superior when com- 
plexed with zinc, thus providing further evidence that the sulfur-containing 
ninhydrin analogues exhibit superior luminescence properties when com- 
plexed with zinc. 

Ramotowski et al. reported on the effectiveness of a series of 1,2-indanedi- 
ones synthesized at the University of Pennsylvania for latent print develop- 
ment. 152 These compounds may be regarded as ninhydrin analogues of a sort. 
Overall, the 5,6-dimethoxy-l,2-indanedione was the most effective. 153 The 
5,6-dimethyl compound (50 mg) was dissolved in 2 mL methylene chloride 
and then diluted with 50 mL methanol. The zinc complex of the reaction 
product gave very good luminescence results with test amino acid spots and 
with test latent prints. Almog’s group further validated 5,6-dimethoxy- 
1,2-indanedione as equal or superior to other ninhydrin analogues and to 
DFO. 154,155 Wilkinson 156 presented spectroscopic evidence that alcohols 
should be avoided as a solvent for the 1,2-indanedione compounds for latent 
print development. Recently, the Almog group reported that computational 
design software might be useful in modeling the potential luminescence 




behavior of Ruhemann’s purple-metal complexes of various ninhydrin ana- 
logues. 157 As noted earlier, Joseph Almog reviewed this material in the pre- 
vious edition 133 and presents the current information in Chapter 5 of this 
volume. 



Development of Latent Prints With Metal 
Ions/Compounds — Physical Developers 

Silver Nitrate Reagent 

Silver nitrate has been used for developing latent fingerprints since 1891 . 1 
The basic principle of this technique is the reaction of silver nitrate with the 
chloride present in the fingerprint deposit. The product of this reaction, silver 
chloride, rapidly turns black on exposure to light. However, because the 
procedure is cumbersome and the background can stain, this method is 
principally of historical interest today. 

Goode and Morris 6 have suggested using a methanolic solution instead 
of the conventional aqueous solution. This method works well with latent 
prints on newspaper and untreated wood. However, silver nitrate reagent 
does not work well with physical evidence that has been stored or exposed 
to high humidity. Under conditions of high humidity, the chloride in the 
latent print deposit migrates by diffusion. Researchers have shown that sig- 
nificant deterioration occurs after 15 days at 60% relative humidity. Prints 
weakly developed with silver nitrate may be enhanced by further treatment 
with dilute physical developer. 9 

Other Silver- Containing Compounds 

Kerr, Westland, and Haque 158 have studied the perchlorate, tetrafluoroborate, 
and hexafluoroantimonate salts of silver as well as silver perchlorate/camphor 
as alternative reagents for silver nitrate solution. These compounds were 
effective, and the studies indicated that the silver salt reaction with the chlo- 
ride in latent fingerprint residue was dependent on the microroughness of 
the surface. 

Physical Developer 

Physical developer enhancement is a photographic process based on the 
formation of silver onto a latent fingerprint image from a ferrous/ferric redox 
couple and metal salt mixture. Goode and Morris 6 have reviewed the early 
work on techniques using “stabilized” physical developer 31 and found that 
physical developer reacts with lipid material present in the fingerprint residue. 
The technique has been used to develop latent prints on paper, nonabsorbent 




surfaces, and pressure-sensitive tapes. It also can be used on objects after 
ninhydrin processing. 6 

Phillips, Cole, and Jones 159 reported that, in actual casework in the FBI 
Latent Fingerprint Section, identifiable latent prints that did not develop with 
ninhydrin were developed on 20% of the specimens processed with physical 
developer (PD). They also found latent prints on postage stamps, the adhesive 
strip on the closure flaps of envelopes, adhesive tapes, the emulsion side of 
photographs, and U.S. currency. The following is a simplified version of the 
procedure reported by them. 



Reagents 

Prewash solution 

Maleic acid 25 g 

Distilled water 1 L 

Redox solution 

Ferric nitrate 30 g 

Ammonium ferrous sulfate 80 g 

Citric acid 20 g 

Distilled water 900 mL 

Surfactant solution 

n-Dodecylamine acetate 3 g 

Synperonic N 4 g 

Distilled water 1 L 

Silver nitrate solution 

Silver nitrate 10 g 

Distilled water 50 mL 



Note: PD working solution: mix 900 mL redox solution, 40 mL surfactant solution, 
and 50 mL silver nitrate solution. 

Procedures 



1. Immerse specimen in maleic acid solution for at least 5 min. 

2. Transfer the specimen from the prewash solution to the PD working 
solution. 

3. Submerge the specimen in PD working solution for approximately 5 
min with a gentle rocking (as long as it takes to develop, but not 
overdevelop, prints). 




4. Rinse the specimen in tap water. 

5. Dry the specimen thoroughly with a temperature-adjustable hair dryer. 

6. Reprocess weakly developed latent prints (low contrast) in PD working 
solution. 

7. Photograph the developed latent print(s). 

8. The visualization of latent prints developed on soiled and darkened 
surfaces can be enhanced by immersing the specimen in a 50% dilu- 
tion of common household bleach. 

Margot and Lennard 9 describe recipes for the original reagent mixtures 
and the Phillips, Cole, and Jones modification 159 just given. In addition, they 
mention a simplified PD, personally communicated to them by Saunders in 
1993 and fully described in Chapter 7 of this volume. The Phillips, Cole, and 
Jones physical developer described above is more stable and produces better 
prints than the Saunders recipe. 

Modified Physical Developer Methods 

In 1989, Saunders and the U.S. Secret Service Forensic Services Division 
reported a new procedure involving the use of colloidal gold with PD. This 
technique was called “multimetal deposition” (MMD). 160 An additional col- 
loidal gold step was used. Collodial gold at pH 3 binds to amino acids, 
peptides, and proteins in fingerprint residue. The bound colloidal gold pro- 
vides a nucleation site around which silver precipitates in the second incu- 
bation step. The following is the procedure for the multimetal deposition 
method: 

Reagents 

Stabilized Physical Developer: Colloidal Gold 

Solution A: Redox 



Ferric nitrate 


33 


g 


Ferrous ammonium sulfate 


89 


g 


Citric acid 


22 


g 


Tween 20 


1 


mL 


Distilled water 


1 


T 



Notes: Dissolve the chemicals in the order listed in 1 L distilled water and then add 
the Tween 20. This solution is stable indefinitely at room temperature. 

Solution B: Silver nitrate 

Silver nitrate 20 g 

Distilled water 100 mb 




Note: Store in a dark bottle at room temperature. 



Working Solution 

Solution A 99 parts 

Solution B 1 part 

Notes: Make just before using: the working solution is stable for only about 15 min. 
Develop prints in the absence of fluorescent lights if possible. 

Preparation of Colloidal Gold 

Stock gold: Prepare a 10% (w/v) solution of tetrachloroauric 
acid in high-quality distilled water. This solution is stable 
indefinitely at room temperature. 

Stock sodium citrate: Prepare a 1% (w/v) solution of sodium 
citrate in distilled water. This solution is stable indefinitely at 
room temperature. 

1. Add 1 mL stock gold solution to 1 L distilled water and bring to a boil. 

2. Gently add 10 mL stock sodium citrate solution and boil gently for 
10 min. The final solution should be the color of port wine. 

3. Stir in 5 mL Tween 20 while solution is still hot and then allow to cool. 

4. Adjust the pH to about 3 with 0.5 M citric acid (usually about 1 mL 
is required). 

5. Restore the solution volume to 1 L. Some volume is lost during the 
boiling steps. 

6. Store the solution in a scrupulously clean glass or plastic container in 
the refrigerator. The solution is stable for several months at 4°C. 

Procedure 



1. If item to be tested is paper, soak it in several changes of distilled water 
for 20 to 30 min. Do not use maleic acid. 

2. Place the item to be tested in the colloidal gold solution for 30 to 120 min. 

3. Rinse the item with distilled water. 

4. Place the item in the silver developer (modified PD working solution) 
for 5 to 15 min. 

5. Thoroughly rinse the item in distilled water. 

6. Air dry the item and photograph the latent prints. 

Saunders found that this procedure worked well with many surfaces and 
materials, such as computer floppy disks, adhesive tapes, metals, papers, 
Styrofoam, credit cards, and glass. It also can be used for specimens that have 




been treated with ninhydrin. In addition, latent prints can be first transferred 
from the specimen surface to a nitrocellulose membrane and then developed. 

In another modification, Knowles 161 reported a radioactive visualization 
method. The developed latent print silver image is first converted to silver 
bromide, which is then reacted with radioactively labeled thiourea to produce 
silver sulfide, and the latent print image can then be recorded by autorad- 
iography. Nolan et al. 162 reported a method employing scanning electron 
microscopy to remove interference from the background. 

Recently, Ramotowski 163 compared a series of commercial and laboratory- 
prepared PD reagents for effectiveness in developing latents on different papers. 
The commercial reagents generally performed adequately, though there can be 
problems with the reagents on occasion. Dilute acetic acid (household vinegar) 
worked about as well as a pre-treatment as the usual maleic acid. Physical 
developers are fully reviewed and discussed by Antonio Cantu in Chapter 7. 

Metal Deposition 

In 1968, Theys et al. 25 reported that it was possible to detect the presence of 
fat films on some surfaces by the selective condensation of metals under 
vacuum. This is often called vacuum metal deposition (VMD). Since that 
time, several metals have been investigated as possible reagents for the delin- 
eation of latent fingerprints. It was reported that a combination of gold 
followed by cadmium treatment produced excellent results. 24 Since cadmium is 
toxic, zinc and the combination of gold/zinc have been suggested. 164 Kent et al. 26 
reported a fairly high success rate with this technique on polyethylene bags. 

Batey et al. 165 indicated the procedure worked well on nonporous paper 
and plastic and could be helpful with older items, such as from older cases. 
Kent and Stoilovic 166 reported successful development of latents with several 
metals using DC sputtering, a variant of VMD. Murphy 167 reported good 
results raising an identifiable latent on a milk carton surface where cyanoacry- 
late fuming alone had not sufficed. 

Migron et al. evaluated a number of metal deposition and vacuum metal 
deposition techniques for detecting both eccrine and sebaceous latent prints 
deposited on cartridge cases prior to firing the cartridges in the appropriate 
firearm. 168 Some identifiable prints could be developed on brass cases, but 
generally, these were difficult surfaces. 



Special Surfaces or Situations 
Enhancement of Bloody Fingerprints 

Special techniques are often required for successfully developing bloody 
latent fingerprints. 6,169-171 Bloody fingerprints can often be found deposited 




on weapons, victims’ bodies, and objects at crime scenes. In many cases, 
these bloody prints require enhancement to increase contrast and make them 
more visible. There are two general categories of chemical reagents that can 
be used to enhance the bloody fingerprints. 

The first category of reagents are those chemicals that react with the 
heme moiety of the hemoglobin molecule of the red blood cells in blood. 
Heme will catalyze an oxidation reaction and convert the reagent to an 
oxidized product that is colored. In the past, reagents prepared using benzi- 
dine were the most popular choice for bloody print enhancement. However, 
benzidine was found to be carcinogenic and thus extremely hazardous. Since 
1974, the use of benzidine has been banned for all practical purposes by the 
federal Occupational Safety and Health Administration. 172 Lee 173 reported 
that a number of safer chemicals, including tetramethylbenzidine, 174 o-toli- 
dine, phenolphthalin, and leucomalachite green, can be substituted for ben- 
zidine in the enhancement schemes. 

The second category of reagents is general protein stains. These chemical 
dye solutions will bind to the protein molecules in blood and yield a colored 
complex. However, since most proteins are water soluble, the bloody finger- 
print proteins have to be denatured and fixed onto the surface before immer- 
sion of the object into the dye solution. The commonly used protein dyes 
such as amido black, 175 ninhydrin, crystal violet, and Coomassie blue 176 have 
been reported to work very successfully in the enhancement of bloody fin- 
gerprints. The preparation of these reagents and procedures for their use 
with latent fingerprints are as follows: 

1. Heme-reacting chemicals 
a. Tetramethylbenzidine 



Reagents 




Buffer solution 




Sodium acetate 


5g 


Glacial acetic acid 


43 mL 


Distilled water 


50 mL 


Stock solution 




3,3',5,5'-Tetramethylbenzidine 


0.4 g 


Buffer solution 


20 mL 


Colloidon-ethanol-ether solution 




Collodion 


30 mL 


Ethanol 


15 mL 


Ethyl ether 


120 mL 




Working solution 

Stock solution 6 mL 

Sodium perborate 0.5 g 

Colloidon-ethanol-ether solution 120 mL 

Note: Mix the stock solution and sodium perborate well, add the colloidon-ethanol- 
ether solution, and mix well again. 

Procedure 



Spray the surface containing the bloody fingerprints two or three times from 
a distance of about 10 in. 

b. Phenolphthalin 



Reagents 

Stock solution 

2g 

20 g 

100 mL 

20 g 



Phenolphthalin 
Potassium hydroxide 
Distilled water 
Powdered zinc 



Note: Reflux until the solution becomes colorless (typically 2 to 3 hr). Store in a dark 
bottle with some zinc powder at the bottom. 

Working solution 

Stock solution 20 mL 

Ethanol 80 mL 

3% Hydrogen peroxide 5 drops 



Procedure 



Apply the working solution to the surface containing the bloody fingerprints 
and allow it to dry. 

c. Leucomalachite green 



Reagents 



Leucomalachite green 
Ethyl ether 



lg 

70 mL 




Glacial acetic acid 

20 to 30% hydrogen peroxide 



10 drops 
5 drops 



Procedure 



Apply the working solution to the surface containing the bloody fingerprints 
and allow it to dry. 

2. Protein dye solutions 

a. Amido black (Naphthol blue black; naphthalene 12B) 



Reagents 




First solution 




Amido black 10B 


0.2 g 


Glacial acetic acid 


10 mL 


Methanol 


90 mL 


Second solution 




Glacial acetic acid 


10 mL 


Methanol 


90 mL 


Third solution 




Glacial acetic acid 


5 mL 


Methanol 


98 mL 



Procedure 



1. Bake article to be examined at 100°C for 30 min or immerse the item 
in methanol for 1 hr. If methanol immersion is likely to damage the 
item, use the alternative (aqueous-based) formula. 

2. Immerse the article into the first solution and agitate it to ensure that 
the entire surface is treated. 

3. Immerse the article into the second solution and agitate it. 

4. Rinse the article in the third solution. 

5. Allow the article to dry and then photograph the print. 

b. Amido black (alternative aqueous-based formula) 

Citric acid stock: 



Citric acid 
Distilled water 



38 g 
2 L 




Note: Combine and stir until citric acid is completely dissolved. 

Developing solution: 

Citric acid stock solution 
Amido black 
Kodak PhotoFlo 600 

Note: Add amido black to stirred solution of citric acid stock, stir 30 min, and then 
add the PhotoFlo. 

c. Crystal violet 



2 L 
2g 



Reagent 

Crystal violet 0.1 g 

Distilled water 100 mL 

Ammonia 

Notes: Dissolve 0.1 g crystal violet in 100 mL distilled water. Stir until the solid is 
completely dissolved. Adjust pH to 7 to 8 with ammonia. 

Procedure 



1. Bake the article to be examined at 100°C for 30 min. 

2. Immerse the article into the solution for 3 min. 

3. Rinse the article with distilled water and allow the surfaces to dry. 

d. Coomassie blue 

Reagents 



Staining solution 

Coomassie brilliant blue R250 0.44 g 

Glacial acetic acid 40 mL 

Methanol 200 mL 

Distilled water 200 mL 

Destaining solution 

Glacial acetic acid 40 mL 

Methanol 200 mL 

Distilled water 200 mL 




Procedure 



1. Bake the article to be examined at 100°C for 30 min. 

2. Immerse the article into the solution for 3 min. 

3. Rinse the article with destaining solution and allow the surfaces to dry. 

e. Crowle’s reagent 



Reagents 

Crocein scarlet 7B 2.5 g 

Coomassie brilliant blue R250 0.15 g 

Glacial acetic acid 50 mL 

Trichloroacetic acid 30 mL 

Distilled water 920 mL 



Procedure 



1. Bake the article to be examined at 100°C for 30 min. This step can be 
omitted with some items. 

2. Immerse the article into the dye solution for 5 to 30 min with constant 
agitation. 

3. Rinse the article with Crowle’s destaining solution (3 mL glacial acetic 
acid in a final volume of 1 L with water) until the background color- 
ation disappears (about 1 min) and allow the surface to dry. 

Note: The staining procedure can he repeated. 

In addition, Whritenour reported that a method using cyanoacrylate fuming 
before Coomassie blue staining enhanced bloody fingerprints on plastic bag 
material. 177 However, McCarthy and Grieve 178 have found that no improve- 
ment was achieved with cyanoacrylate fuming in most situations. With glass 
and metal surfaces, cyanoacrylate preprocessing is harmful for further pro- 
cessing with Coomassie blue, Crowle’s reagent, and amido black dye. Warrick 
reported good results in developing a bloody print on a cotton sheet surface 
with an amido black staining solution used in conjunction with digital 
enhancement of the resulting developed print. 179 Jaret, Heriau, and Donche 180 
investigated the feasibility of transferring heme reagent-developed prints 
onto photographic papers or other similar media and noted that only leu- 
cocrystal violet and leucomalachite green treated prints could be transferred. 




Zauner 181 noted that on a rare occasion, a friction ridge print could be 
developed on denim. 

Lee and Gaensslen have compared all the methods available for the 
enhancement of bloody fingerprints. 7 It was found that the heme-reacting 
chemical reagents, such as tetramethylbenzidine, phenolphthalin, o-toli- 
dine, and leucomalachite green, are extremely sensitive to the presence of 
blood and will yield positive results with dilutions of blood as low as 1 part 
in 1 million. On the other hand, general protein dye solutions, such as 
Crowle’s reagent, amido black, crystal violet, and Coomassie blue, show a 
sensitivity toward blood that generally falls in the 1 part in 1 thousand 
dilution range. A disadvantage of techniques involving the dye solution 
staining technique is that articles containing latent prints have to be directly 
immersed in the solution. To prevent the bloodstain from dissolving in the 
solution, the article has to be baked in an oven at 100°C for 3 to 5 min to 
denature and fix the bloodstain on the surface. In addition, most dye 
solutions are made with organic solvents or are soluble under acidic con- 
ditions, making them unsuitable for use on certain surfaces. Hunter 182 
described successful development of an identifiable print on gloves after 
25 years with Coomassie blue. 

Allman and Pounds communicated to Margot and Lennard 9 in 1991 and 
1992 that they favored the use of diaminobenzidine (DAB) for bloody print 
enhancement. Treatment of the bloody latent prints is by immersion, first in 
a solution of 2% 5-sulfosalicylic acid for about 2 min followed by a distilled 
water wash. Next, the prints are treated in a solution consisting of (a) 0.1 g 
DAB in 10 mL distilled water; (b) 90 mL of 0.1 M phosphate buffer, pH 7.4; 
and (c) 0.5 mL of 30% H 2 0 2 solution. Stoilovic 183 noted that blood prints 
on porous surfaces can be visualized using DFO and Polilight with a 590 
bandpass viewing filter. Use of DFO does not preclude the subsequent use 
of colored protein stains. 

It is known that when liquid blood coagulates (clots), the serum and 
blood cells separate. A straw-colored liquid, the serum fraction, forms 
around the solid red mass, the blood cell fraction. If a finger touches 
coagulated blood that has not dried and then deposits a print on a surface, 
the resulting “bloody” fingerprint may be composed mainly of serum, 
mainly of coagulated red cells, or of both. These possibilities have signifi- 
cant implications for choosing the optimal method of bloody fingerprint 
enhancement. The best method for a particular bloody print should be 
based on an understanding of the nature of the bloody print and the 
mechanism of transfer. Although not strictly having to do with latent print 
development, another issue that sometimes arises is the order of deposition 
of blood vs. fingerprints. 184,185 




Development of Latent Prints on Tapes or Sticky Surfaces 

The development of fingerprints on adhesive tape has always been a challenge 
for latent fingerprint examiners. In 1981, Ishiyama 186 reported the successful 
development of fingerprints on the adhesive side of cellophane tape using 
Coomassie brilliant blue 250. Koemm 187 reported the use of gentian violet 
(crystal violet) to develop latent prints on the sticky side of tape. Arima 188 
reported using aqueous solutions of crystal violet or Victoria page blue for 
polyvinyl chloride (PVC), cloth, Kraft paper, or cellophane tapes as long as 
these tapes were not of a dark color. Latent fingerprints on the sticky surfaces 
of adhesive tapes could be successfully developed. He also suggested the use 
of a fluorescent dye, Mikephor, for colored or black electrical tape. Latent 
prints can be visualized by treatment with Mikephor BS, a fluorescent bright - 
ener, and subsequently viewed under UV light. Arima also found that the 
fluorescent reagents o-phthalaldehyde and 8-anilino-l-napthalene sulfonic 
acid were equally effective. Martin developed identifiable prints on the sticky 
side of black tape by painting an ash-gray powder suspended in PhotoFlo 
solution onto the surface then gently rinsing with water. 189 Similarly, 
Sneddon 190 and Paris 191 described the successful use of mixtures of detergents 
and black powders for sticky tape surfaces, and Burns 192 used a product called 
“Sticky Side” powder (available in Japan) with PhotoFlo with good results 
on the items tested except the sticky side of black electric tape. 

Wilson and McCleod 193 proposed an alternative method for the visualiza- 
tion of fingerprints on black tape using crystal violet and photographic paper. 
Tucker 194 described a modified crystal violet method for processing latent prints 
on black electrical tape. The following is the general outline of the procedure: 

Reagents 

Stock solution 

Crystal violet 
Ethyl alcohol 

Working solution 

Stock solution 
Distilled water 



1.5 g 
100 mL 



10 mL 
500 mL 



Procedure 



1. Brush the adhesive side of the tape with the crystal violet working 
solution using a camel-hair brush. 

2. Dry the tape surface with a hot hair dryer. 




3. Expose the tape surface to a high-intensity photo lamp until the latent 
prints have developed. 

4. Photograph the developed latent prints. 

5. With black tape, transfer the developed latent print onto photographic 
paper by the following procedure. 

a. Place the developed tape between two pieces of RC photographic 
paper with the emulsion side of the photographic papers facing the 
tape to form a “sandwich.” 

b. Place the sandwich between two pieces of 1/8-in. -thick blotter 
paper. 

c. Heat the blotter paper at low temperature using an iron. 

d. Photograph the transferred fingerprint. 

Margot and Lennard 9 use a stock solution of 5 g gentian violet and 10 g 
phenol (very toxic) in 50 mL ethanol. The working solution is a 1:25 dilution 
of stock into water. The processed latents are transferred onto photographic 
paper. Other recipes we have seen for the phenol-based reagent use the same 
stock solution as Margot and Lennard, but the working solution is a 1:100 
dilution of stock into water. 

Teuszkowski and Loninga 195 have found that the emulsion side of pho- 
tographic paper often sticks to the adhesive side of the tape and suggested 
an alternative procedure for processing latent prints on the sticky side of 
black tape. Taylor and Mankevich 196 reported using a silver protein staining 
procedure to develop latent prints on tape. This method was found to be 
very effective when used in conjunction with gentian violet. Hollars, Trozzi, 
and Barron described a procedure involving treatment with Ardrox in 
detergent solution that was said to work well on dark-colored, sticky sur- 
faces where gentian violet worked poorly. 197 Bratton and Gregus compared 
gentian violet, a commercial “Sticky Side” powder, and a black powder in 
detergent suspension on a series of latent prints on various tapes. 198 Prints 
in the study were characterized as “initial,” “sebaceous,” and “eccrine.” The 
black powder in detergent suspension worked best on the “eccrine” prints, 
that are apparently not well developed by gentian violet. Howard 199 used 
basic fuchsin processing on black electric tape that does not respond well 
to gentian violet; 20 mg basic fuchsin (Aldrich Chemical product was pre- 
ferred in limited comparison study) was dissolved in 400 mL methanol or 
water, and the test item was immersed for 50 sec to 1 min before drying 
and examination under laser light. 

Martin 200 reported moderate success in developing latents on smooth 
glossy surfaces that had been transferred there from the sticky surfaces of 
tapes, frosted cellophane tape was the most efficient transfer medium. 




Detection of Latent Prints on Skin 

Over the years, various procedures have been suggested for the visualization 
and recovery of latent fingerprints on human skin. Methods such as dusting 
with magnetic powder, 201 Kromekote card lifting, 24 electronography, 24 iodine- 
silver plate transfer, 202 ' 204 laser detection by inherent luminescence, 205 dusting 
with fluorescent powder or evaporative staining with fluorescent dyes fol- 
lowed by laser examination, 206 and Super Glue fuming have all been investi- 
gated. 207 Allman and Pounds reviewed this subject in 1991. 208 

The iodine-silver plate transfer method was at one time considered to 
be a practical technique for the recovery of latent prints on skin. 209 In this 
method, the area of skin with the suspected latent print is first fumed with 
an iodine fuming gun. Once the latent print image is developed, the image 
is transferred onto a silver plate, exposed to strong light, and evaluated. 

Cyanoacrylate fuming and dusting with Mars red fluorescent powder or 
staining with Rhodamine 6G followed by laser examination have recently 
been shown to be somewhat successful. Delmas 210 studied the use of lumi- 
nescent magnetic powder in conjunction with cyanoacrylate fuming and laser 
examination on cadavers. Five cadavers were examined after intentionally 
placing latent prints on body surfaces, and identifiable latent prints were 
recovered in four of the cases. 

The following is the general procedure for processing latent fingerprints 
on the human body by the combination method of cyanoacrylate fuming, 
dusting with fluorescent powder, and laser examination: 

1. Place a suitable tank, box, tent, or casket over the cadaver. 

2. Put approximately 0.5 to 1.0 g Super Glue into the fuming chamber. 

3. Place 500 mL hot water into a beaker and put this in the fuming 

chamber to increase the humidity. 

4. Fume the body for approximately 30 min to 1 hr. 

5. Prepare the Rhodamine 6G magnetic powder: 

a. Dissolve 0.1 g Rhodamine 6G in 50 mL methanol. 

b. Add 100 g black magnetic powder to the rhodamine solution. 

c. Heat the mixture with constant stirring until dried. 

d. Grind the dried mixture to fine powder. 

6. Dust the body with the rhodamine-coated magnetic powder. 

7. Examine the dusted area under laser light or any other light sources. 

8. Photograph the developed latent print(s). 

Sampson has described systematic methods for latent prints on skin. 211,212 
The temperature differential between the lifting medium and body (10 to 
16°C), where the medium is warmer, is said to be key to success. Various 




lifting media were used, followed by Super Glue fuming. Ruthenium tetrox- 
ide, 1 02 various modifications of Super Glue 64,213 (including experiments using 
an animal model) 214 and transfer to polyethylene terephthalate (PET) 
sheets, 215 and casting techniques 30 have all been mentioned. 

Wilkinson and Watkin 91 described a europium chelate (TEC) designed to 
exploit the narrow emission band of the rare earths using intramolecular energy 
transfer to overcome its poor absorption characteristics and successfully applied 
this technique to cyanoacrylate-developed latents on cadaver skin under certain 
conditions. In comparing this procedure to others, however, they generally got 
the most consistent results with an iodine-benzoflavone technique. 216 

Generally, hairless areas of smooth skin on a fresh body are more likely 
to yield identifiable latent prints. However, there has yet to be a single, 
effective procedure developed, and success rates are very low. 

Development of Latent Fingerprints on Wet Surfaces 

Morris and Wells patented a technique for developing latent prints on wet 
surfaces, especially wet paper, that used finely divided particles in a surfactant 
solution. 31 This reagent is called stabilized physical developer (SPD; see Phys- 
ical Developer on page 136). 217 SPD has been found to offer considerable 
potential for the detection of latent prints on surfaces that have been exposed 
to water. SPD reagent consists of a solution containing ferrous ammonium 
sulfate and ferric nitrate, silver nitrate, citric acid buffer, and two surfactants: 
laurylamine acetate and Lissapol. The development is done under tungsten light 
to reduce random background deposition over the entire surface. 

Development of Latent Fingerprints on Other Special Surfaces 

Periodically, there have been reports on special techniques or variations of exist- 
ing techniques to improve development of latent prints on unusual surfaces, 
such as incendiary bottles, 218 ' 220 stones, 221 firearms and firearms-related evi- 
dence, 96,168,222 ' 225 computer components in gaming machines, 226 deer antlers, 227 
and aluminum foil. 228 Levi and Leifer 229 described a procedure to create contrast 
between latent prints on glass bottles and the glass for photography. 

Luminescence/Fluorescence — Laser and Alternative Light 
Source Methods for Latent Print Enhancement 

Laser Light and Alternative Light Sources 

The ability to use laser illumination to detect latent fingerprints is one of the 
most significant developments in this field ever. The routine use of laser 




illumination is often done in conjunction with metal salt post-treatment of 
ninhydrin-developed latents. Accordingly, much of the information was pre- 
sented starting on page 127. Here, the underlying principles and some more 
recent developments are discussed further. 

As early as 1937, scientists suggested that alternative light sources (other 
than room light) could be used for the enhancement and visualization of 
latent fingerprints. High-intensity lamps, UV light sources, lasers, and xenon 
arc lamps have been utilized in the development of latent prints 16 ' 19,77,230,231 
and have produced better latent print images than regular room light. 

Dalrymple, Duff, and Menzel 230 first reported the technique of laser 
detection of latent fingerprints by their inherent luminescence. Subsequently, 
a number of alternative procedures were suggested. Various fluorescent pow- 
ders such as Mars red, hi-intensity fingerprint powder, Red Lake C, and 
naphthol red B (2 / -naphtholazo-l-bromo-2-naphthol-l / -sulfonate) have 
subsequently been employed to enhance the detection sensitivity of the laser 
procedure. Other fluorigenic dyes, such as coumarin 6, Rhodamine 6G, 
Rhodamine B, Aquabest orange fluorescent pigment, phenothiazine, Nile 
Blue A perchloride, and 3,3'-diethylthiatricarbocyamine iodine, have also 
been used to enhance laser light detection of latent prints. 16 " 20 Initially, it was 
recognized that inducement of the intrinsic fluorescence of latent fingerprint 
residue required wavelengths shorter than were available in any commercial 
lasers. Thus, use of compounds with desirable excitation and emission wave- 
lengths that would also adhere to fingerprint residue or interact with ninhy- 
drin- or cyanoacrylate-processed latent prints greatly extended the 
applicability of laser processing. 16,17,20,75,148,232 These chemicals react or interact 
preferentially with components in fingerprint residues to form luminescent 
reaction products. Of all the different strategies tried, post-treatment of 
ninhydrin-developed latent prints with zinc chloride has proved the most 
robust for laser processing. 77,124 Other types of lasers such as dye lasers and 
copper vapor lasers have also been used for latent print detection. A review 
of the use of lasers for the detection of latent prints can be found in the first 
edition of this book. 131 

Bramble et al. showed that shortwave UV illumination produced as the 
fourth harmonic of a Nd:YAG laser (266 nm) gave good results with a series 
of sebaceous prints on white surfaces, yielding more prints of good quality 
than several visible luminescence methods. 233 Ben-Yosef et al. reported sim- 
ilar results, although noting that the technique was primarily applicable to 
searching textiles and other substrata for biological fluids. 234 Shortwave UV 
illumination did not give good luminescence results with eccrine prints. 
These methods take advantage of the intrinsic fluorescence properties of 
latent fingerprint residue and may be preferable to more widespread methods 




under certain circumstances. The Bramble group has also used thin-layer 
chromatography of actual latent fingerprint residue to help identify the flu- 
orescing species. 235 In this context, it is also of interest that high-energy 
discharges yield fluorescence in latent print residue 236,237 and that the respon- 
sible component may well be a lipid. Related to this is a corona discharge 
technique described by Halahmi et al. 238 

Menzel 131 has noted that laser detection of latent print residue can exploit 
three properties associated with luminescence: intensity, color, and lifetime. 
He and collaborators investigated the use of time-resolved imaging methods 
to take advantage of the fact that background luminescence is typically 
shorter (by orders of magnitude) than fingerprint residue signal. 239 A similar 
approach has been mentioned in connection with supressing background 
illumination when using portable laser light at crime scenes. 240 

Some trivalent lanthanides display long lifetime luminescence character- 
istics and will complex with Ruhemann’s purple. 241 Menzel recognized in 
1997 that this feature made them good candidates for latent print detection 
and amenable to both optical filtering and time-resolved imaging as 
well. 242 244 This approach in effect substitutes a lanthanide (usually Eu) for 
zinc in complex with Ruhemann’s purple. Unlike the Zn complexes, the 
lanthanide ones require UV excitation, however, and the coupling of other 
compounds to the complex to take advatange of intramolecular energy trans- 
fer to improve the luminesence have been explored, especially by Wilkinson 
and her collaborators. 91,92,245,246 Allred and Menzel described a novel Eu bio- 
complex (with EDTA) to enhance Ruhemann’s purple luminescence from 
latent print residues. 105 

In 1983, Kobus, Stoilovic, and Warrener at the Forensic Science Research 
Unit of Australia developed a modified xenon arc lamp. 123 About the same 
time, the “Quaser” light source was developed by the Scientific Research and 
Development Branch of the U.K. Home Office, and the “Lumaprint” light 
was designed by Watkin at the National Research Council of Canada. It was 
found that the modified xenon arc lamp could produce results comparable 
to those obtained with the laser in the detection of latent prints developed 
with either NBD-C1 or ninhydrin followed by zinc chloride. 140 Currently, 
there are several different alternative light sources commercially available 
under the trade names Unilite, Luma-Lite, and Polilight. In addition, some 
very good results have been reported by German using a reflected UV imaging 
system (RUVIS) originally developed by scientists at the National Police 
Agency of lapan and commercially available. 247 The so-called alternate or 
alternative light sources have sufficient versatility in their illumination band- 
width adjustments to be good alternatives to lasers when used with appropriate 
dyes in the various latent development techniques and with appropriate viewing 
filters. 




The most recent developments in novel approaches to latent print devel- 
opment involve photoluminescent nanocrystals or nanocomposites by Men- 
zel and collaborators. 248 250 Practical methods based on this interesting 
approach have yet to be fully developed. The subject is reviewed and explored 
in Chapter 6. 



Miscellaneous Methods 



Nolan et al. 251 reported that latent prints developed by small particle reagents 
are easily imaged by the back-scattered electron image mode of the scanning 
electron microscope (SEM). Low SEM magnifications have permitted the 
recording of single complete fingerprints on checks, newsprint, and other 
surfaces. In addition, X-ray radiography and infrared microscopy have also 
been suggested for the detection of latent fingerprints. 252,253 

Graham and Gray described an electronography technique in 1966. 24 A 
latent print was first dusted with fine lead powder and subsequently bombarded 
with X-rays from high-energy sources; the emissions were then detected by 
photographic emulsions. It was reported that that technique has been used 
successfully in developing latent print human skin. 24,254 It also worked well on 
multicolored surfaces, background interferences being totally eliminated. 255 

A few techniques have been proposed that were based on now dated 
serological techniques. 256 ' 258 One study 259 looked at a bacteriological tech- 
nique for the detection of fingerprints. 



Systematic Approaches to Latent Print Processing 

There have been hundreds of techniques for the development and visualiza- 
tion of latent fingerprints reported in the literature. Each of the methods has 
its advantages and performed well under certain conditions. The application 
of the correct technique for a particular surface or given set of conditions is 
extremely important. The application of more than one technique or reagent 
for the detection of latent prints can often increase the number of prints 
found or improve the quality of those already developed. However, it is 
imperative that reagents are applied in a systematic and correct order. Use 
of a wrong or inappropriate procedure might actually destroy the latent print 
evidence and obviate any chance for visualization by another technique. 

Beginning in 1985, several investigators suggested different logical schemes 
for the sequential development of latent prints. 260 ' 262 An excellent manual of 
fingerprint development technique was published in 1986 that contained vari- 
ous systematic process charts for developing latent fingerprints. 260 Lennard and 
Margot 8,9 conducted detailed studies of the various chemical reagents available 




Visual Examination 

l 

Photography 

I 

Enhancement Methods 

J 1 

Physical Chemical Luminescence 

Methods Methods Methods 



Photography 

Figure 4.2 General approach to developing latent fingerprints. 

and developed sequential procedures for improved visualization of latent fin- 
gerprints on porous and nonporous surfaces. 

Figures 4.2 through 4.7 represent some of the systematic approaches that 
have been successfully employed by the Connecticut State Police Forensic 
Science Laboratory. Figure 4.2 represents a general approach for the detection 
of latent fingerprints. Figure 4.3 is a scheme for the enhancement of bloody 
fingerprints. Figure 4.4 shows the approach for the detection of latent fin- 
gerprints on nonporous surfaces. Figure 4.5 is the procedure used for visu- 
alization of latent fingerprints on greasy or waxed surfaces. Figure 4.6 shows 
the systematic approach for the detection of latent fingerprints on adhesive 
tape. Figure 4.7 is the procedural scheme for the development of latent fin- 
gerprints on paper products. These logical schemes serve primarily as sug- 
gested orders for the application of a series of techniques to the processing 
of latent prints by examiners. They are not to be regarded as complete or 
perfect. The systematic approaches should be continuously modified and 
refined as new procedures, chemical reagents, and approaches are developed. 

The fingerprint field has witnessed revolutionary change in the last 30 
years, especially in the development of novel methods for the development 
and enhancement of latents. Many of the newer methods are based on clever 



Visual Examination 



I 

I 

Amido 

Black 

I 

I 

I 

I 

I 

I 

I 

L _ 



I 

Photography 

I 

TM B -- 



Ninhydrin 

I 

I 

+ 

Heat 



► Photography 



Figure 4.3 Systematic approach for developing bloody fingerprints. 



applications of chemistry and physics to fingerprint science. Fingerprint 
examiners continue to play a primary role in crime scene and criminal 
investigations, but will increasingly need greater knowledge of and training 
in chemistry, luminescence methods, imaging, and computer technologies 
as the field moves forward. 




Visual Examination 
Photography 




DRY 



WET 



I 

Super Glue Fuming 

i 

Powder Dusting 
or 

Gentian Violet Stain 
or 

Luminescent Dye Stain 

I ^ Laser or Alternate 
Light Excitation 



I 

Small Particle 
Reagent Spray 
or 

Physical Developer 
or 

Modified Physical Developer 

i 

— ► Photography 



Figure 4.4 Systematic approach for developing latent fingerprints on nonporous 
surfaces. 



Visual Examination 
Photography 

Iodine Fuming -► 7 ’ 8 Benzoflavone 

Fixation 




Figure 4.5 Systematic approach for developing latent fingerprints on greasy or 
waxy surfaces. 




Visual Examination 

i 

Photography 

I 

Iodine Fuming — Fixation — ► Photography 

I 

8-Anilinonaphthalene-1 -sulfonate — ► Photography 

I 

Super Glue Fuming 

I 



Laser or Alternate 
Light Excitation 



Photography 



Figure 4.6 Systematic approach for developing latent fingerprints on adhesive 
tapes. 




Visual Examination 



l 

Non-Adhesive Side 



I 

Photography 



Adhesive Side 



I i 

Super Glue Fuming Crystal Violet Staining 

i 



Chemical Dye Staining 
Luminescent Chemicals 

I 

Laser or Alternate 
Light Excitation 



Modified Physical Developer 

i 



Photography 



Figure 4.7 Systematic approach for developing latent fingerprints on porous 
surfaces, including paper. 




References 



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203. Gray, C., The detection and persistence of latent fingerprints on human skin: 
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204. Gelinas, N. L., The iodine silver transfer method for obtaining fingerprints 
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218. Shelef, R., Levy, A., Rhima, I., Tsaroom, S., and Elkayan, R., Development of 
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220. Elkayam, R., Rhima, I., and Shelef, R., Development of latent prints from 
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221. Donche, A. and Loyan, S., Development of latent prints on stones. /. Forensic 
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222. Migron, Y. and Mandler, D., Development of latent fingerprints on unfired 
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223. Barnum, C. A. and Klasey, D. R., Factors affecting the recovery of latent prints 
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224. Freeman, H. N., Magnetic fingerprint powder on firearms and metal car- 
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225. Sampson, W. C., An inquiry into the methodology of preserving and devel- 
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226. Shipp, E., Davenport, W., and Togneri, E., Latent print and the gaming 
industry. /. Forensic Ident., 45, 504, 1995. 

221 . Otis, J. C. and Downing, A., Development of latent fingerprint impressions 
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228. Wiesner, S. and Springer, E., Improved technique for recovering fingerprints 
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229. Levi, J. A. and Leifer, A., Improving contrast in photographs of latent finger- 
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230. Dalrymple, B. E., Duff, J. M., and Menzel, E. R., Inherent fingerprint lumi- 
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231. Duff, J. M. and Menzel, E. R., Laser assisted thin layer chromatography and 
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232. Menzel, E. R., Posttreatment of latent prints for laser development. Forensic 
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233. Bramble, S. K., Creer, K. E., Gui Qiang, W., and Sheard, B., Ultraviolet lumi- 
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234. Ben- Yosef, N., Almog, J., Frank, A., Springer, E., and Cantu, A. A., Short UV 
luminescence for forensic applications: design of a real-time observation 
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299, 1998. 

235. Jones, N. E., Davies, L. M., Brennan, J. S., and Bramble, S. K., Separation of 
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236. Meylan, N., Lennard, C. J., and Margot, P. A., Use of a gaseous electrical 
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237. Davies, L. M., Jones, N. E., Brennan, J. S., and Bramble, S. K., A new visibly- 
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238. Halahmi, E., Levi, O., Kronik, L., and Boxman, R. L., Development of latent 
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239. Murdock, R. H. and Menzel, E. R., A computer interfaced time-resolved lumi- 
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240. Li, W., Ma, C., Jiang, H., Wu, C., Lu, Z., Wang, B., and Lin, B., Laser finger- 
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241 . Alaoui, I. M. and Menzel, E. R., Substituent effects on luminescence enhance- 
ment in europium and terbium Ruhemann’s purple complexes. Forensic Sci. 
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242. Mekkaoui, A. I. and Menzel, E. R., Spectroscopy of rare earth-Ruhemann’s 
purple complexes. /. Forensic Sci., 38, 506, 1993. 

243. Allred, C. E., Lin, T., and Menzel, E. R., Lipid-specific latent fingerprint detec- 
tion: fingerprints on currency. /. Forensic Sci., 42, 997, 1997. 

244. Allred, C. E., Murdock, R. H., and Menzel, E. R., New lipid-specific, rare 
earth-based chemical fingerprint detection methods. /. Forensic Ident., 47, 
542, 1997. 




245. Misner, A., Wilkinson, D., and Watkin, J., Thenoyl Europium Chelate: a new 
fluorescent dye with a narrow emission band to detect cyanoacrylate devel- 
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43, 154, 1993. 

246. Wilkinson, D. A. and Misner, A. H., A comparison of thenoyl europium 
chelate with ardrox and rhodamine 6G for the fluorescent detection of 
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247. German, E. R., Reflected Ultraviolet Imaging System Applications, Almog, J. 
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249. Menzel, E. R., Takatsu, M., Murdock, R. EE, Bouldin, K., and Cheng, K. EE, 
Photoluminescent CdS/dendrimer nanocomposites for fingerprint detection. 
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250. Bouldin, K. K., Menzel, E. R., Takatsu, M., and Murdock, R. EE, Diimide- 
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developed fingerprints using scanning electron microscopy, in Proceedings of 
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252. Wilkinson, R. D., The use of infrared microscopy in detecting latent finger- 
prints, personal communication, 1979. 

253. Lail, H. A., Fingerprint recovery with electronography. Police Chief, 42, 34, 
1975. 

254. Mooney, D. G., Fingerprints on human skin. Ident. News, 27, 5, 1977. 

255. Winstanley, R., Recovery of latent fingerprints from difficult surfaces by an 
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256. Ishiyama, I., Orui, M., Ogawa, K., and Kimura, T., The determination of 
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257. Okada, T. and Ohrui, M., On new method of identifying blood types from 
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258. Hussain, J. I. and Pounds, C. A., The detection of latent fingerprints by bio- 
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259. Harper, D. R., Clare, C. M., Heaps, C. D., Brennan, J., and Hussain, J., A 
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260. Home Office Scientific Research and Development Branch (HOSRDB). Man- 
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Fingerprint Development 
by Ninhydrin and 
Its Analogues 



5 



JOSEPH ALMOG 



Contents 



Chemical Development of Latent Fingerprints 
Ninhydrin: The Universal Reagent for Fingerprints on Paper 
History and General Properties of Ninhydrin 
Reaction with Amino Acids 
Ninhydrin as a Latent Fingerprint Reagent 
Formulation Variations 
The Influence of Temperature and Humidity: 

Modes of Application 

Secondary Treatment with Metal Salts: Fingerprint Detection 
Aided by Lasers and Alternate Light Sources 
Ninhydrin Analogues 

Structural Modifications: BenzoJ/] ninhydrin and Related 
Compounds 

l,8-Diazafluorene-9-one (DFO) 

1,2-Indanedione 

References 

Despite the wide variety of reagents for chemical development of latent 
fingerprints on paper, many of which have been reported and investigated 
over the past decade, none has been found with sufficient advantages to 
supplant ninhydrin. 

Ninhydrin reacts with amino acids and other components of palmar 
sweat that yield amino acids when broken down. The final color of the 
developed prints is usually purple (Ruhemann’s purple). Full development 
may take several days or even weeks, but the reaction can be accelerated by 
heat and moisture. The most recent formulation uses the solvent HFE7100 
as the carrier, after the former highly successful formulation was banned by 
the “Montreal Protocol on Substances that Deplete the Ozone Layer.” 

The art of fingerprint development has made great progress since the 
discovery that latent fingerprints on paper can be visualized by ninhydrin. 



There were four principal milestones in this evolution: (1) the introduction 
of the nonflammable formulation, NFN (nonflammable ninhydrin, which is 
now banned); (2) the introduction to fingerprint development of lasers and 
alternate light sources; (3) the secondary treatment with metal salts to pro- 
duce fluorescent impressions; and, (4) the preparation and examination of 
ninhydrin analogues, whose crowning achievements were the introduction 
of DFO and the recent discovery of the potential of 1,2-indanedione. These 
processes remarkably improved the ability of law-enforcement agencies to 
detect latent fingerprints on porous surfaces such as paper and cardboard. 
Indeed, over the past few years many reports have appeared in the forensic 
science literature describing actual cases of fingerprint detection that would 
have been impossible only a few years ago. Ninhydrin is currently used in a 
sequence in advanced fingerprint laboratories. To achieve best results, it is 
applied after DFO and before PD. 

The aim of this chapter is to survey the use of ninhydrin as a fingerprint 
reagent, with emphasis on progress in recent years. Two sections, “Compar- 
ison with Other Reagents” and “Miscellaneous Considerations,” that 
appeared in the previous edition of Advances in Fingerprint Technology do 
not appear separately this time. 

Chemical Development of Latent Fingerprints 

Latent fingerprints on porous surfaces can be visualized by numerous chem- 
ical methods. Many of these can be regarded as purely theoretical because 
they have no practical use in the forensic science laboratory. On the other 
hand, no single technique for recovering latent prints has universal applica- 
tions under all circumstances, and the choice of method may vary from case 
to case. 1,2 In its narrow definition, the chemical development of latent fin- 
gerprints is expressed by a visual chemical reaction between the reagent and 
one or more of the constituents of human perspiration, to yield a colored, 
luminescent, or radioactive product. In this manner the ridge detail becomes 
visible and the prints can be photographed and further manipulated. 

Amino acids are the most desirable substrate of the palmar sweat com- 
ponents to be developed on paper. They are always present in human per- 
spiration and they produce colored and luminescent products with a variety 
of reagents. Due to their high affinity for cellulose, they do not migrate with 
age (like urea or inorganic salts) and can be developed even after a long 
period of time. Cases have been reported in which latent prints have been 
detected and identified on paper specimens known to have been handled 
several years previously. 3,4 Amino acids on paper can be visualized by a variety 
of chemical reagents such as fluorescamine, 5 ' 7 alloxan, 3,8 o-phthalaldehyde 6,7 





I 

Figure 5.1 2,2-Dihydroxy-l,3-indanedione (ninhydrin). 

and other aromatic vicinal dicarboxaldehydes, 9,10 7-chloro-4-nitrobenzo- 
2-oxa- 1,3-diazole (NBD-chloride) and its derivatives, 12 14 together with a 
long list of ninhydrin analogues, particularly 1,8-diazafluorenone (DFO) and 
most recently also 1,2-indanedione (see text); but from the forensic scientist’s 
perspective, ninhydrin is undoubtedly the most important. 1 ’ 3 ’ 7,15,16 



Ninhydrin: The Universal Reagent for Fingerprints on Paper 
History and General Properties of Ninhydrin 

Ninhydrin (Figure 5.1) was first prepared by Ruhemann 17 in an attempt to 
oxidize 1-hydrindone (II) to 1,2-diketohydrindene (III, Figure 5 . 2 )*. Instead 
of the expected product, he obtained another compound, triketohydrindene 
hydrate, known today as ninhydrin. On the basis of his experimental work, 
Ruhemann proposed the structure of the new substance as 2,2-dihydroxy- 
1,3-indanedione (Figure 5. 1). 17,18 

It is interesting that Kaufmann had previously reported the preparation 
of a compound with the same structure, but his compound did not have 
ninhydrin properties. 19 

Ninhydrin is a crystalline solid that is soluble in water and other polar 
solvents. It crystallizes from ethanol as pale yellow prisms. When the solid is 
heated to 125-130°C, it changes to pink, red, or reddish brown. At 130-140°C, 



* The more common names for these compounds are 1-indanone and 1,2-indanedione, 
accordingly. These names will prevail throughout this chapter. 



NMe2 





Figure 5.2 Ruhemann's first preparation of ninhydrin. (From Ruhemann, S., 
J. Chem. Soc., 97, 2025, 1910.) 



-H 2 0 
OH 



O 

I IV 

Figure 5.3 Formation of 1,2,3-indanetrione, the anhydrous form of ninhydrin. 

it becomes deep purple-red and melts sharply, with decomposition at 241°C. It 
becomes red when exposed to sunlight and should be stored in a cool place. 20 

Upon heating in vacuum or treatment with thionyl chloride, ninhydrin 
loses water to give dark red needles of 1,2,3-indanetrione (IV, Figure 5.3), the 
anhydrous form of ninhydrin. 21 Ninhydrin reduces Fehling’s solution 17 and 
forms phthalic anhydride upon heating in a current of air. 21 Its most important 
activity is obviously the reaction with amino acids to form a colored product 
(“Ruhemann’s purple”), as explained in the next chapter section. 

It is interesting that in forensic chemistry there is also a totally different 
use of ninhydrin — the detection of drugs on thin-layer chromatography 
(TLC) plates. Various drugs develop spots of different colors when TLC plates 





o 



HN- 

HN- 




V 



RCHCOOH 

+ | 

nh 2 




Figure 5.4 Formation of murexide (VI) in the reaction between alloxan (V) and 
amino acids. 



are sprayed with a concentrated solution of ninhydrin. The mechanism of 
this reaction remains unclear. 22 

A comprehensive review of ninhydrin and its chemical and physical 
properties was published by McCaldin in I960. 20 Of the two more recent 
reviews on ninhydrin and related compounds, the one by Joullie et al. is of 
particular importance because it covers not only general chemistry, but also 
forensic aspects. 23,24 A comprehensive review of vicinal polycarbonyl com- 
pounds has appeared very recently. 25 



Reaction with Amino Acids 

Ruhemann discovered and correctly interpreted ninhydrin’s most useful reac- 
tion with alpha amino acids. 18 He was impressed by the close similarity 
between ninhydrin and another cyclic triketone, alloxan, whose reaction with 
alpha amino acids gives carbon dioxide, an aldehyde, and a blue compound, 
murexide (Figure 5.4). Ruhemann showed that the purple product of the 
ninhydrin reaction (later named after him, Ruhemann’s purple) was the 
ninhydrin analogue of murexide. 17,18 ' 26 ' 28 

Despite the fact that the ninhydrin reaction has been used extensively to 
detect and estimate amino acids, its mechanism has not been fully under- 
stood until recently; hence, it has given rise to a number of theories. There 
was even a controversy regarding the type of amino acids that undergo this 
reaction. Although Ruhemann claimed that not only alpha, but also beta 
amino acids, give the purple-blue color when treated with the reagent, it has 
been stated by others in later years that only alpha amino acids are reactive 
in this manner. 29,30 The general nature of the reaction, however, gave an 
indication of its probable course: if the reaction is as general as stated, it is 
likely that the purple color is the same for all amino acids and that only a 
fragment of the amino acid involved is contained in the colored compound. 20 
A detailed discussion of the mechanism is beyond the scope of this chapter. 

The currently acceptable general mechanism for the ninhydrin reaction, 
as suggested by Friedman and Williams in 1974, 31 is outlined in Figure 5.5. 
Ninhydrin (I) tautomerizes to 1,2,3-indanetrione (IV), which forms a Schiff ’s 






Figure 5.5 The mechanism of formation of Ruhemann's purple (X). (From Fried- 
man, M. and Williams, L.D., Biooiganic Chem., 3, 26 7, 1974.) 

base with the amino acid. The ketimine formed (VII) undergoes decarbox- 
ylation and cleavage, yielding the aldehyde and an intermediate amine (IX). 
Condesation of the amine (IX) with another molecule of ninhydrin (I) fol- 
lows to form the chromophore, Ruhemann’s purple (X). A slight modifica- 
tion of this mechanism was suggested in 1986 by Grigg and co-workers. 32 
They indicated that the intermediate imine (VIII) exists as a 1,3-dipole (XI, 
Figure 5.6), and that 1,3-dipole form is also the structure of the protonated 
form of Ruhemann’s purple (XII, Figure 5.7). 

The deprotonated form, which is the colored product, Ruhemann’s pur- 
ple (X), has a highly stabilized aza-allylic chromophore that is responsible 
for the color (XIII, Figure 5.7). A summary of the mechanistic approaches 
was published by Bottom and co-workers. 33 Grigg’s modification, which 
involves the formation of an azomethine ylide, is the currently accepted 
mechanism. 34 

Ninhydrin as a Latent Fingerprint Reagent 

Shortly after the discovery of the ninhydrin reaction with amino acids, sci- 
entists noticed that many common materials form blue-colored products 
upon reaction with ninhydrin. In 1913, three years after the first report on 
ninhydrin, Abderhalden and Schmidt in Germany wrote: 35 



o 




XI 

Figure 5.6 The 1,3-dipole form of the intermediate imine in the ninhydrin 
reaction. 




XU Xffi 



Figure 5.7 Protonated (XII) and deprotonated (XIII) forms of Ruhemann's purple. 
(From Grigg, R., Malone, J.F., Mongkolaussavaratana, T., and Thianpatanagul, S., 
/. Chem. Soc., Chem. Commun., 421, 1986. 

Ninhydrin is a valuable reagent for the detection of the non-biuret dialyzable 
amino acids. Various tissues, milk, urine, saliva, blood, plasma, serum, 
lymph, cyst contents, fresh eggs, albumin, fresh and boiled meat, and sweat 
contain substances which dialyze and react with ninhydrin. The fact that 
sweat gives an intense reaction is of importance in carrying out the test. 
Caution must be taken that nothing is touched which later comes in contact 
with the reagent. 

In the following years, ninhydrin became a common reagent in various 
biochemical and medical test methods. Following the introduction of chro- 
matographic techniques in the early 1940s, ninhydrin was routinely used to 
locate amino acids on chromatograms. Thus, it is somewhat surprising that 
despite its usage over the years and the oft-repeated admonition against 
touching chromatograms or other test material to be exposed to ninhydrin, 
only in 1954 was ninhydrin recognized as a latent fingerprint reagent. Two 
Swedish scientists, Oden and von Hofsten, were the first to suggest the use 
of ninhydrin as a means to develop latent fingerprints. 36 A year later, Oden 
patented the process. 37,38 

As mentioned previously, one of the outstanding features of ninhydrin 
compared with other chemical processes for paper is the fact that amino 




acids, the substrate for its action, are stable and do not appear to migrate 
with age. Ninhydrin is, therefore, a most suitable reagent for revealing latent 
prints on porous surfaces such as paper, cardboard, raw wood, and plaster- 
board. Its use is relatively simple, but achieving good results requires some 
skill and experience. The process can be carried out with no substantial 
hazard to health,* provided that a few straightforward precautions are 
observed. 

Formulation Variations 

The ninhydrin formulations and development conditions recommended by 
the first few groups of researchers varied widely and did not provide maxi- 
mum detection efficiency. 42 There was no agreement on factors such as con- 
centrations, solvents, temperatures and heating times, pH, modes of 
application, and humidity conditions. In 1955, Oden recommended a for- 
mulation composed of ninhydrin solution in acetone or ether that also con- 
tained acetic acid to enhance sensitivity. 37 Since then, a number of studies 
have been published in which one or more of the aforementioned factors 
were varied. Until 1974, the solvent list included acetone, diethyl ether, ethyl 
alcohol, isopropanol, petroleum ether, and acetone-water mixtures. Ninhy- 
drin concentrations varied between 0.2 and 1.5%, and the concentration of 
acetic acid varied between 0 and 4%. 1,42 In general, little or no improvement 
over Oden’s original formulation was achieved. Crown’s formulation in 
1969, 43 however, was of particular importance to questioned documents 
examiners. It was based on petroleum ether, which does not dissolve ink. It 
suffered, however, from one major disadvantage — high flammability. As a 
matter of fact, most other formulations were also flammable, particularly 
those containing diethyl ether. Indeed, fires in forensic science laboratories 
have been reported as a result of using these solvents. 44 Ether is also liable to 
explode and its use in solutions or spray is extremely hazardous! 

In 1974, a most remarkable breakthrough in optimizing the formulation 
of the ninhydrin reagent was reported by two Englishmen, Morris and Goode. 
They described an improved ninhydrin reagent based on another nonpolar 
solvent, 1,1,2-trifluorotrichloroethane (known also as Fluorisol, Arklone P, 
Freon 113, or CFC113). Their formulation, which has since been named 
“NFN formulation” (nonflammable ninhydrin), is nonflammable, nontoxic, 
and does not dissolve ink on documents. It is highly sensitive and can be 
applied by dipping or swabbing. 42 A modified composition, containing the 



* In 1989, it was reported that use of a surgical marking pen containing ninhydrin to 
indicate hest areas on the skin caused eczema in three female patients. 39 More recently, a 
fingerprint technician developed symptoms of rhinitis as a result of handling papers 
immersed in a solution containing ninhydrin. Medical tests confirmed that it was an allergic 
reaction to ninhydrin. 40 - 41 




less volatile 1,1,2-trichloroethane, was recommended by J.R. Morris for 
spraying. 45 A standard working solution of NFN contains about 0.5% nin- 
hydrin (w/v), 0.9% acetic acid (v/v), and 1.8% ethyl alcohol, in Fluorisol. 
Ethyl alcohol is required to dissolve the solid ninhydrin, and acetic acid 
provides the acidity required to balance the alkalinity of some papers. 46 

The authors also mentioned some disadvantages of the new formulation 
in their original paper. It forms background coloration on papers with a 
particular surface coating, such as banknotes, some checks and postal money 
orders, and rag-based writing papers, and on surfaces that have been exposed 
to high humidity. NFN reagent is not suitable for application to nonabsorbent 
surfaces such as plastics or ceramics. 42 An attempt to further improve the 
formulation was reported in 1984 by Tighe. The solution suggested, “Freon 
plus two,” is also based on Fluorisol, but instead of ethyl alcohol it contains 
methyl alcohol and ethyl acetate. 47 Margot, Lennard, and co-workers reported 
that the addition of acetic acid improves upon the results obtained by the 
“Freon plus two” formulation. In 1986, they reported that the main advantage 
of this formulation is the ease of its preparation; however, in all other respects 
it resembles the original NFN reagent. 48 

NFN formulation was the recommended composition in the Fingerprint 
Development Techniques Guide, published in 1986 by the Scientific Research and 
Development Branch (SRDB), of the British Home Office. The editor, T. Kent, 
recommended the use of this reagent for paper, cardboard, raw wood, and 
plasterboard. In his chapter on ninhydrin, Kent surveyed all the operational 
aspects of this technique, including the preparation of solutions, necessary lab- 
oratory equipment, the mode of application, and safety requirements. 49 

The NFN formulation has become a general-purpose reagent, applicable 
to a wide range of paper and other surfaces, with minimal background effects. 

The production of Fluorisol was banned within the European commu- 
nity, the U.S., and many other countries since the end of 1994 under the 1992 
Brussels Amendment to the “Montreal Protocol on Substances that Deplete 
the Ozone Layer.” In 1993, Watling and Smith suggested the use of heptane 
as an alternative carrier to Freon 113. 50 W.O. Jungbluth, of the U.S. Army 
Laboratory, reported in the same year that Genesolv 2000, a hydrochloro- 
fluorocarbon, was an acceptable replacement for Freon 113, “provided the 
evidence does not possess . . . handwriting for possible examination.” 51 Good 
results with heptane, comparable to those obtained with Freon 113, were 
reported also by Hewlett and Sears, but they did not recommend its use for 
fingerprint development due to the high flammability of the solvent. 52 Super- 
critical carbon dioxide was reported as a potential substitute for Freon 113 
by Hewlett et al. in 1996. 53 

A recent formulation that appears to satisfy all the requirements for 
fingerprint work is based on the work of Hewlett, Sears, and Suzuki from 




1997, which uses the solvent HFE7100 as the carrier. 54 HFE7100 is a mixture 
of two hydrofluoroethers: 50 to 70% methylnonafluoroisobutyl ether and 30 
to 50% methylnonafluorobutyl ether. It is a volatile, nonpolar, nontoxic, and 
nonflammable liquid and provides a safe and effective replacement to Freon 
113 in the ninhydrin process. The working solution contains 0.5% ninhydrin 
in HFE7100 carrier that also contains ethanol, ethyl acetate, and acetic acid. 55 

The Influence of Temperature and Humidity: 

Modes of Application 

Crown, 43 the 1976 FBI guide for the development of latent impression, 4 and 
Olsen 1 all recommend the following order for visualizing latent fingerprints 
on porous surfaces: treat with iodine fumes, then with ninhydrin, and finally 
with silver nitrate solution. This simplified procedure more or less exhausted 
the forensic scientist’s knowledge until the mid-1970s. Due to the great 
progress in fingerprint techniques since then, a more sophisticated procedure, 
which provides much better results, is now practiced by advanced fingerprint 
laboratories. Figure 5.8 outlines the flowchart for fingerprint visualization 
on paper and cardboard, recommended in 1998 by the PSDB in England. 55 
It distinguishes between wet and dry paper and it involves visual examination 
under white light, inherent fluorescence examination, and a sequence of three 
chemical steps: DFO, then ninhydrin, and finally physical developer (PD). 
According to their concept, which is also the standard system in many other 
advanced laboratories, ninhydrin treatment is considered a “primary route,” 
while DFO and PD are “special routes.” (PD is a primary route for wet paper). 
The Forensic Science Service (FSS) in London, whose Serious Crime Unit 
(SCU) applies perhaps the widest variety of fingerprint development meth- 
ods, 56 uses a similar sequence: light examination, followed by DFO, ninhydrin 
and PD, and, finally scanning electron microscopy. The SCU still uses the 
NFN formulation for ninhydrin, but the introduction of HFE7100 has 
started. 57 

Ninhydrin can be applied by several methods: spraying a fine mist, dip- 
ping into a solution, or swabbing a solution onto the surface. Less conven- 
tional modes are exposure to ninhydrin fumes, 58 direct treatment with 
ninhydrin crystals without a solvent, or pressing a paper towel impregnated 
with ninhydrin solution against the item to be developed. 1 Only the first three 
methods (spraying, dipping, and swabbing) are used extensively. There is no 
general agreement on the method of choice, but dipping seems to be the 
most common technique for laboratory work. 42,49,55 ’ 59 Spraying is recom- 
mended for extremely fragile paper items such as tissue paper, which can fall 
apart if dipped into solution or tear if swabbed. 1 Swabbing is the least desir- 
able mode of application because the swabbing action tends to smear ink on 
documents. 1 



PAPER and CARDBOARD 

and for porous surfaces including matt emulsion paint; 
not for plastic coated papers or wax 




Figure 5.8 Flowchart for fingerprint visualization on paper and cardboard. (From 
Manual of Fingerprint Development Techniques, 2nd ed., T. Kent, Ed., PSDB, 
Home Office, (U.K.), 1998. With permission.) 

In most cases, treatment after ninhydrin includes the application of heat. 
It is clear, however, that elevated temperatures also accelerate the formation 
of background discoloration. Thus, if the speed of development is not a 
crucial factor, for better contrast it is advisable to let the latent prints develop 
at room temperature in the dark, although the process may take days or even 




















weeks. 42,46,49 Exposure times and temperatures vary considerably among the 
various groups. Oden and von Hofsten suggest heating to 80°C for a few 
minutes. 36 O’Hara recommends a much higher temperature (140°C). 60 
Crown suggests processing at 100°C 43 for his petrol ether formulation, 
whereas Kent recommends 80°C and warns against heating certain items 
above 50°C. 49 It is clear, however, that if time permits, room-temperature 
development will always give the best “signal-to-noise” ratio, and this is the 
recommended technique. 46 

A number of groups have studied the influence of humidity on the quality 
of developed prints. In the mid-1960s, both Crown 61 and Mooney 62 reported 
that the presence of water vapors in the processing oven improves results. 
Moenssens found that best results are obtained during periods of high relative 
humidity and that “slow cure” at room temperature is preferable. 63 A study 
by Lesk established that optimum development is obtained by processing the 
ninhydrin-treated prints at 65 to 80% relative humidity. 64 In tests conducted 
by the U.S. Army Criminal Investigation Laboratory, the best results were 
obtained when ninhydrin-treated documents were maintained at 80% 
humidity and a temperature only slightly above room temperature. 1 The 
Royal Canadian Mounted Police (RCMP) laboratories in Ottawa recommend 
the use of a saturated sodium chloride solution in the development chamber 
to maintain the 75% relative humidity that is most desirable for the ninhydrin 
process. 65 A steam iron can be effectively used to accelerate the ninhydrin 
development of prints. The iron must not touch the paper surface, but be 
moved over the surface at a distance of 1 to 2 cm. Olsen, however, reports 
better contrast in humidity cabinet development. He also suggests not to use 
the iron method on cardboard or coated paper because steam condenses on 
such surfaces. 1 Development by placing the object over boiling water has 
been suggested by Rispling, 66 who also advises to watch the exhibit closely 
until coloration ceases. In 1976, Connor reported the results of a collaborative 
study that examined the effect of a steam iron on ninhydrin-treated prints 
on bond and newsprint papers. His study shows that latent prints are devel- 
oped by this method within minutes after the ninhydrin treatment and that 
the mode of the ninhydrin application has very little effect on the results. 67 
Consequently, the Association of Official Analytical Chemists (AOAC) 
adopted this method that same year. 68 

In their late 1970s studies, Morris 69 and then Jones and co-workers 70,71 
reached the firm conclusion that steaming and heating after ninhydrin treat- 
ment of papers can lead to a significant increase in the quality and contrast 
of the marks revealed. Even when this improvement does not occur, there is 
no disadvantage in using this method; thus, they confidently recommend it 
for general use. The use of a microwave oven for steaming after ninhydrin 
treatment is recommended by Margot, Lennard, and co-workers. 72 




Specially designed cabinets for chemical development of fingerprints 
under controlled conditions of temperature and humidity have become a 
major tool in most advanced forensic laboratories. 

Secondary Treatment with Metal Salts: Fingerprint Detection 
Aided by Lasers and Alternate Light Sources 

Despite the fact that ninhydrin is regarded as “the latent fingerprint examiner’s 
workhorse,” 73 it suffers from the following disadvantages and limitations: 

1. The chemical process is slow. 

2. Many paper samples contain ninhydrin-positive materials that give 
rise to the formation of intense background coloration and can 
obscure the developed prints. 42 ’ 46 ’ 74 * 

3. Sensitivity is not always sufficiently high. Not all individuals excrete 
sufficient perspiration to leave identifiable prints using those methods 
known today. 43,46 ’ 74 

4. The contrast of ninhydrin-developed prints is often insufficient 46,48 on 
certain dark surfaces. 

5. Prints developed with ninhydrin are not permanent. (There is debate 
among fingerprint practitioners as to whether or not this is a real 
problem. 43,59 ) 

Hence, ninhydrin application to a document does not guarantee the devel- 
opment of latent fingerprints, although it may be known that the document 
was indeed touched by a certain person. 43 Considerable research efforts have 
been made toward the improvement of some of these drawbacks since the 
first application of ninhydrin to casework. In the beginning, most researchers 
focused on attempts to improve the formulations and working conditions. 
The crowning achievement of this approach was the development of the NFN 
formulation in 1974. 42 In 1977, the discovery of the potential of lasers for 
forensic science applications opened a new era in fingerprint technology. In 
that year, Dalrymple, Duff, and Menzel reported that latent fingerprints on 
various surfaces could be visualized by illumination with an argon-ion laser 
and observation through an appropriate filter. 75 Later studies showed that 
the percentage of latent prints detectable by their inherent luminescence under 
laser illumination was not very high, and researchers started to explore the 
possibility of combining lasers with fingerprint reagents. 12 This approach led to 
the next leap forward in the use of ninhydrin for fingerprint development. 



* These background colors arise from the presence of natural organic constituents in the 
raw materials or from the various sizing or coating materials used to improve the surface 
properties (e.g., rag-based high-quality writing paper , 46 bank notes [where melamine has 
been used as a plasticizer], and some checks and postal money orders ). 72 




In 1981, German reported that laser examination of ninhydrin-developed 
prints may reveal details unseen under conventional room lighting, 73 and a 
year later Herod and Menzel showed that weak ninhydrin-developed prints 
could be enhanced by examining them with a dye laser. 76 This observation 
was of limited practical value because it entailed the addition of a dye laser 
to the argon laser; the improvement in many cases was too small. It was the 
other discovery of this group, reported in the same year, that brought about 
substantial progress in the ninhydrin technique: the conversion of the purple 
ninhydrin-treated marks to fluorescent prints that can be detected under 
laser illumination. 77 Amino acid chemists have known for a long time that 
Ruhemann’s purple spots on chromatographic plates change their color to 
red or orange after they have been treated with salts of certain metals such 
as nickel, cadmium, and zinc. 78 ' 80 In fingerprint chemistry, this process was 
suggested as a means to overcome contrast problems on colored surfaces and 
also to improve the stability of the marks. 45,74 Herod and Menzel, who investi- 
gated this phenomenon, found that the marks not only changed color upon 
treatment with metal salts, but also became highly fluorescent under the argon 
laser. In their 1982 article, they wrote that “a pronounced improvement in 
detectability is observed when ninhydrin-treated latent fingerprints are sprayed 
with a solution of zinc chloride and subsequently subjected to argon laser exam- 
ination.” 77 This discovery quickly made an impact on many fingerprint labora- 
tories. Many prints that could not be developed by conventional manner 
emerged after zinc chloride treatment and laser examination. The method also 
gave positive results on some nonporous surfaces that had been considered 
unsuitable for ninhydrin treatment. 77 Spectral data of the complex that is formed 
between Ruhemann’s purple and zinc chloride were also reported in the same 
work. The 488-nm line of the argon laser was found ideal for excitation of the 
orange complex, which absorbs at about 485 nm and emits at 560 nm. 

Since this discovery, luminescence procedures, in which nonfluorescent 
samples are converted into highly fluorescent products, have become an 
essential tool in most fingerprint laboratories. Analytical methods based on 
luminescence are much more sensitive — up to four orders of magnitude 
more sensitive than corresponding methods based on absorption. 81 * This 
perception has led to the development of “fingerprint-dedicated” argon 
lasers, and also alternative light sources that are cheaper, lighter, and easier 
to maintain. The potential use of the copper-vapor laser was discussed as 
early as 1982. 82,83 A year later, Warrener and co-workers reported the use of 
a xenon arc lamp equipped with a filter for fingerprint development by NBD- 
chloride, 13 and by ninhydrin followed by zinc chloride. 84 This group indicated 



* Although the term "luminescence" includes both fluorescence and phosphorescence, 
most forensic applications involve only fluorescence, and this is what is predominantly 
implied throughout this chapter. 




the importance of cooling the object (to the temperature of liquid nitrogen, 
-200°C) during the examination, which greatly enhances luminescence. 
Under such conditions, results are similar to those obtained with a 20-W 
argon laser. They recommend the use of xenon arc lamps by police forces 
that cannot afford argon lasers. 84 Since then, many more alternate light 
sources dedicated to fingerprint visualization after treatment with ninhydrin 
and zinc chloride have become commercially available. To name but a few: 
Tuma-Lite in Canada, 85,86 Quaser in the U.K, 87,88 Omniprint in the U.S, the 
Australian Polilight (formerly Unilite), 89,90 and the Kawasaki FDW-200i in 
Japan. 91 Frequency-doubled Nd:YAG lasers were also considered for finger- 
print use. 92 The efficiency of all these systems increases remarkably when the 
sample is cooled by liquid nitrogen during the fluorescence examination. The 
use of cadmium instead of zinc was suggested by Stoilovic, Warrener, and 
co-workers in 1986. In their studies, the cadmium complexes showed certain 
advantages over zinc complexes. They were less prone to development con- 
ditions and gave stable and reproducible results under extreme conditions 
of heat and humidity. Drawbacks of the cadmium reagents include toxicity 
and the need to cool the item to observe luminescence; results, however, were 
extremely rewarding. 42,93 The suggested procedure is to dip the ninhydrin- 
developed prints into a cadmium nitrate solution, let the solvent evaporate, 
cool it with liquid nitrogen, and then examine it with an appropriate light 
source. (The actual advantage of the use of cadmium vs. zinc salts is contro- 
versial. It was discussed in depth by Menzel and Warrener. 94 ) 

X-ray diffraction studies by Lennard et al. on the cadmium complex of 
Ruhemann’s purple show that each molecule of the complex contains one 
cadmium atom bound to one unit of Ruhemann’s purple 95 (XIV, Figure 5.9), 
as opposed to the 1:2 ratio previously suggested. 92,96 Water was shown to be 
an essential component in the formation of the fluorescent complex, which 
explains the need for moisture in fingerprint enhancement by this tech- 
nique. 95 Later crystallographic studies by Davies et al. also clarified the struc- 
ture of the zinc complex. 97,98 



Ninhydrin Analogues 

Structural Modifications: Benzo[/]ninhydrin and 
Related Compounds 

Until the early 1980s, most attempts to improve the ninhydrin technique 
involved modification of formulations and working conditions. The chemical 
reagent remained unaltered. A totally different approach was demonstrated 
by Almog et al. in 1982. It was based on the perception that ninhydrin’s special 
reactivity with amino acids had been discovered by Ruhemann by sheer 




fluorescent complex 




Figure 5.9 Formation of Ruhemann's purple-metal complex. (From Lennard, 
C.J., Margot, P.A., Sterns, A., and Warrener, R.N., J. Forensic Sci., 32, 597, 1987. 
With permission.) 



coincidence, and that it was not the outcome of any theoretical design. They 
proposed a modification of the ninhydrin molecule in an attempt to enhance 
the color and fluorescence of the corresponding Ruhemann’s purple com- 
plexes. It was assumed that compounds analogous to ninhydrin, containing 
the same active moiety — the cyclic vicinal triketone but with different 
groupings on the aromatic ring — might also react with amino acids to give 
colored products, and some of them could become new fingerprint reagents 
with improved properties. Expansion of the conjugated system and intro- 
duction of electron-donating or electron-withdrawing substituents can, in 
principal, modify the color by increasing the molar absorption coefficient 
(epsilon), or by shifting the absorption maximum towards longer or shorter 
wavelengths (red or blue shift). They named this group of compounds “nin- 
hydrin analogues.” Their initial experiments included the preparation of 
three ninhydrin analogues, all of which gave colored products with amino 
acids. One analogue in particular, benzoj/] ninhydrin (Figure 5.10), showed 
great promise. It developed latent fingerprints as dark green impressions, 
with a sensitivity similar to that of ninhydrin. 99 * The ability to develop a 
print of a specific color and then treat the developed print with zinc chloride 
to afford a complex that exhibits fluorescence or another color would aid in 
print visualization on a variety of backgrounds. In 1985, Menzel and Almog 
reported that the zinc complex of benzo[/]ninhydrin-developed prints 
showed luminescence properties that were superior to those obtained from 
the zinc complex of prints developed with ninhydrin. 92 This result stimulated 
interest in the preparation of ninhydrin analogues, which would serve as 
more sensitive fingerprint reagents. In 1986, Lennard et al. synthesized and 



* Benzo[f]ninhydrin was prepared for the first time in 1957 by Meier and Lotter, who also 
reported the formation of a dark green color upon reaction with amino acids. They did not 
characterize the color spectroscopically and this reaction had no practical use. 100 






Figure 5.10 Ninhydrin (I) and some of its analogues that were prepared and 
evaluated as fingerprint reagents: I, ninhydrin; XV, benzo^ninhydrin; XVI, 5- 
methoxyninyhdrin; XVIII, 5-methylthioninhydrin ; XIX, thieno[/]ninhydrin; XX, 
5-(2-thienyl)ninhydrin ; XXI, naphtho[/]ninhydrin. 

tested nine ninhydrin analogues for their ability to develop fingerprints and 
to afford luminescent complexes upon treatment with metal salts. 101 ' 102 The 
reagent 5-methoxyninhydrin (XVI, Figure 5.10) was found to yield prints 
that exhibited much more intensive fluorescence than with ninhydrin-devel- 
oped prints. The advantages of 5-methoxyninhydrin were discussed in detail 
by Almog and Hirshfeld. 103 In 1987, it was adopted for operational use by 
Israeli Police and had an immediate and remarkable success in solving an 
extortion case. 103 A synthetic route to 5-methoxyninhydrin was also reported 
by this group. 104 * That same year, Joullie, Cantu, and co-workers reported a 
different synthetic pathway to benzo[/] ninhydrin that affords higher yield 
than obtained by the former group. 105 

Further studies in this series showed that the ninhydrin structure is not 
essential for fingerprint development, and that vicinal triketones of other 
types also react in the same manner. The most important prerequisite is a 
cyclic structure. Thus, compounds such as alloxan (V) and tetramethylcyclo- 
pentanetrione (XVII, Figure 5.11) also give a positive reaction with amino acids 
and with latent fingerprints. 106 Menzel, in 1989, demonstrated a time-resolved 



* 5-Methoxyninhydrin has become commercially available under the name 2,2-dihydroxy- 
5-methoxy-l,3-indanedione (Aldrich Chemical Co., catalog no. 34 100-2). 



o 





Figure 5.11 Vicinal cyclic triketones other than ninhydrin that also give chro- 
mogenic reaction with amino acids: V, alloxan; XVII, 4,4,5,5-tetramethylcyclo- 
pentanetrione. 

imaging system to suppress background luminescence of certain papers that 
may obscure fingerprint fluorescence. This was based on the observation that 
the lifetimes of natural paper luminescence are very short, whereas the life- 
times of the fingerprint fluorescence can be controlled by application of 
appropriate fluorogenic reagents. Thus, when europium trichloride is used 
as the metal salt in the secondary treatment stage, and benzo[/] ninhydrin as 
the primary reagent, the fluorescence of the complex has a much longer 
lifetime than the background. By using a pulsed laser such as a copper-vapor 
laser or specially arranged argon laser and appropriate electronic gating, it 
is possible to see only the fingerprint fluorescence after the background 
luminescence has long decayed. 107 

Although the laser-induced fluorescence of latent fingerprints developed 
with ninhydrin analogues greatly improved ninhydrin methodology, there 
were still considerable difficulties in applying them to practical work. Most 
of the analogues were not commercially available and the cost of those few 
that were available was extremely expensive. A number of research groups, 
particularly the joint effort of Joullie in Philadelphia and Cantu in Washing- 
ton, D.C., have started to explore the possibility of developing efficient, cost- 
effective syntheses of ninhydrin analogues and to evaluate them. This group 
has not only devised very elegant synthetic routes to ninhydrin analogues, 
but it has also produced some very efficient analogues. The list of ninhydrin 
analogues that have been synthesized and evaluated since 1980 contains 
nearly 100 compounds. Most of these give a chromogenic reaction with amino 
acids and some are also fluorogenic. Particularly good results have been obtained 
with ninhydrin analogues containing divalent sulfur, such as 5-methylthionin- 
hydrin, 109 111 (XVIII), thieno[/]ninhydrin, m (XIX), and 5-(2-thienyl)ninhy- 
drin, 112 (XX, Figure 5.10). They exhibit good chromogenic as well as fluorogenic 
properties with amino acids and with latent fingerprints. Sulfur derivatives of 
ninhydrin and ninhydrin analogues have been reported by Menzel and 
Mekkaoui Alaoui to produce intensive luminescence after secondary treatment 
with europium and terbium salts. 113 " 115 Selenium-containing analogues have 



been prepared and evaluated as fingerprint reagents by Della, Kobus, and co- 
workers. 116,117 Other analogues that have been prepared and tested as finger- 
print reagents are amino- and hydroxy-ninhydrins and a pyridine analogue 
(Almog et al. 118,119 ), arylated ninhydrins (Joullie et al. 111,120 ' 122 and Della 
et al. 116,117 ), a thiophene analogue (Joullie, Cantu, and co-workers 123 ), two 
“ninhydrin dimers” (Joullie etal. 124 ), a pyrazine analogue (Frank etal. 125 ), 
and a phenyldiazo-ninhydrin (Della and Taylor 116 ). Alkyl ninhydrins were 
synthesized to obtain better solubility in nonpolar solvents (Hark and 
Joullie 122 and Pounds 1265 . The effect of various alkoxy groups on the solubility 
and fluorogenicity of the analogues was recently reported by a joint team of 
the National Research Institute of Police Science and the Pharmaceutical 
Institute of Tohoku University in Japan. 127 

A list of ninhydrin analogues that have been prepared and evaluated can 
be found in Petrovskaia’s Ph.D. thesis. 112 A comprehensive list of analogues, 
containing more than 80 compounds that have been published over the years, 
not only for fingerprint research, was recently composed by Hark. 128 

A joint team of the British PSDB and the Israel Police recently reported 
that the high hopes of benzo[/] ninhydrin had not been fulfilled. Despite the 
better contrast and fluorescence produced by this compound, the total num- 
ber of latent prints that could be visualized by it was less than with ninhy- 
drin. 129 Also, the longer homologue of ninhydrin, naphthoj/] ninhydrin (XXI, 
Figure 5.10), reported by Hallman and Bartsch gave disappointing results. It 
did not produce any visible reaction with amino acids. 130,131 Elber et al. have 
recently used computational methods to study Ruhemann’s purple and anal- 
ogous compounds. They suggest a theoretical explanation for the limited 
success in improving the color of the developed prints. Based on theoretical 
considerations, they have also designed new analogues that might afford 
more intense colors with latent fingerprints. Their best “candidates” are 
modified ninhydrin molecules, in which one or two of the side carbonyl 
oxygens are replaced by either divalent sulfur or by methylene groups. 132 
These compounds have not yet been prepared. 

Ninhydrin derivatives that are not exactly “analogues” but that are also 
used in fingerprint visualization are ninhydrin-hemiketals. Compounds of 
this type have been prepared by Takatsu et al. in Japan to substitute ninhydrin 
for fingerprint development on thermal paper which is contaminated by the 
conventional ninhydrin formulations. The rationale behind their study is 
that, like ninhydrin, its hemiketals might react with latent fingerprints, but 
they are much more soluble than ninhydrin in nonpolar solvents. Indeed, 
the hemiketal derived from ninhydrin and 3,5,5-trimethyl-l-hexanol 
(Figure 5.12) in hexane solution developed good prints on thermal paper 
without any contamination. 133 It is currently used by forensic science labo- 
ratories in Japan. 91 



o 




Figure 5.12 Alkoxyninhydrin (ninhydrin hemiketal) currently used in Japan for 
fingerprint visualization on thermal paper. (From Takatsu, M. et al., Development 
of a new method to detect latent fingerprints on thermal paper with o-alkyl derivative 
of ninhydrin, Report of the National Institute of Police Science, Japan, 44, 1, 1991.) 





Figure 5.13 1,8 -Diazafluorene-9-one (DFO) (XXII) and the anhydrous form of 
ninhydrin (IV). Notice the resemblance of the active moiety in both molecules. 



l,8-Diazafluorene-9-one (DFO) 

In 1990, as a part of their search for new ninhydrin analogues, Grigg, Pounds, 
and co-workers modified the ninhydrin molecule even further. In addition 
to “regular” ninhydrin analogues, they also prepared and evaluated com- 
pounds that maintained only the essential functional group — the five-mem- 
bered ring with one carbonyl in the center and two adjacent dipoles on both 
of its sides. One compound on their list, l,8-diazafluorene-9-one [diazaflu- 
orenone or DFO, (XXII, Figure 5.13)], reacted with amino acids and with 
latent fingerprints on paper to afford both color and fluorescence. With 
amino acids it provided a red pigment whose structure closely resembled 
that of Ruhemann’s purple 134 (Figure 5.14). 

A thorough mechanistic study by Wilkinson in Canada supported Grigg’s 
assumption 134 that the NH proton in the product is mobile between the 
nitrogen atoms. It also indicated the formation of a transient hemiketal as 
the active species in this reaction. 135 








XII 



Figure 5.14 The red pigment formed by the reaction of DFO with amino acids 
(XXIII). Notice the resemblance to Ruhemann's purple (XII). (From Grigg, R., 
Mongkolaussavaratana, T., Pounds, C.A., and Sivagnanam, S., 1,8-Diazafluorenone 
and related compounds. A new reagent for the detection of alpha amino acids and 
latent fingerprints, Tetrahedron Lett., 31, 7215, 1990.) 



Latent fingerprints that were treated with DFO displayed only a faint red 
color but they luminesced brightly under green light (absorption maximum 
at about 470 nm and emission maximum at about 570 nm 136 ). There was no 
need for a secondary treatment with metal salt to induce luminescence, and 
the total number of identifiable prints developed by it was considerably 
higher than with ninhydrin. These properties very quickly made DFO the 
most important fluorogenic reagent for latent fingerprints. The best formu- 
lation still uses Fluorisol as the main carrier solvent, but a thorough study 
has been initiated to find an acceptable alternative. 137 The formulation pro- 
posed by the PSDB is a 0.025% solution of DFO in Fluorisol containing 3% 
methanol and 2% acetic acid. Optimal development conditions are 20 min 
at 100°C and no humidity. 55 Stoilovic’s modification also included chloro- 
form in the mixture, and the final concentration of DFO was 0.04%. 138 A 
non-CFC formulation based on petrol ether as the main carrier was suggested 
by Margot and Lennard. 139 Its main disadvantage is high flammability. 
Another non-CFC formulation, based on fert-butylmethyl ether, was sug- 
gested by Geide. 140 Conn, Lennard, and co-workers found that secondary 
treatment with metal salts had only a negligible effect on the luminescence 
although metal complexes had been formed. 141 

Several attempts to obtain an improved DFO reagent by modifying its 
molecule (DFO analogues) were unsuccessful. 134 There has been no follow- 
up to the observation of Frank and Handlin in 1993 142 that two compounds 
structurally related to DFO, one of them dipyridyl ketone, produce very 
strong fluorescence when reacted with amino acids. On the other hand, some 
ketals derived from DFO to increase its solubility in nonpolar solvents do 
react with latent fingerprints but not as well as DFO. 143 

At present, DFO is considered the best fluorogenic fingerprint reagent 
for paper and porous surfaces, and it is used as the first stage of the chemical 
sequence: DFO, ninhydrin, and PD. 




MeO 




Figure 5.15 1,2-Indanedione (III) and some of its analogues that give fluorogenic 
reaction with amino acids and with latent fingerprints: III, 1,2-indanedione; XXIV, 
5,6-dimethoxyindanedione; XXV, 6-methoxy-l,2-indanedione (and other isomers); 
XXVI, 6-hydroxy- 1,2-indanedione (and other isomers). (From Hauze, D.B., Petro- 
vskaia, O.G., Taylor, B., Joullie, M.M., Ramotowski, R., and Cantu, A.A., J. 
Forensic Sci., 43, 744, 1998; Wiesner, S., Optimization of the Indanedione Process 
for Fingerprint Development, M.Sc. thesis, Casali Institute of Applied Chemistry, 
The Hebrew University of Jerusalem, Israel, 2001.) 



1,2-indanedione 

The most recent, remarkable discovery in this field is 1,2-indanedione. To 
develop new routes to ninhydrin analogues, Joullie, Cantu, and co-workers 
synthesized and evaluated another class of compounds closely related to 
ninhydrin: 1,2-indanediones (Figure 5.15). These compounds were prepared 
and described in the chemical literature prior to Joullie, but never before had 
they been examined as potential amino acid or fingerprint reagents. 

Methanolic solutions of various 1,2-indanediones were applied to amino 
acid spots on filter paper. They afforded light pink stains that fluoresce 
brightly upon illumination with green light. 144,145 Secondary treatment with 
zinc nitrate increased the fluorescence dramatically, particularly when 
5,6-dimethoxy-l,2-indanedione (XXIV, Figure 5.15) was used as a reagent. 
The fluorescence is stronger than with DFO-treated stains. Heat and humid- 
ity also have an augmentative effect on the fluorescence, but cooling to liquid 
nitrogen temperature is unnecessary. 

Initial experiments with latent fingerprints under similar conditions 
afforded brightly fluorescing fingerprint images. 145 

The effects of further structural modifications in the indanedione series 
were studied by Almog et ah; in their opinion, 1,2-indanedione itself, even 
without secondary treatment, is at least as sensitive as DFO. 146 They also 
devised a novel synthetic route to some indanediones 147 that could not be 
prepared by the original method developed by Cava et al. 148 

The first positive experiments with indanediones were carried out in 
methanolic solutions. Nevertheless, Petrovskaia and Joullie, 112 Wilkinson, 149 
and Wiesner et al. 150 recommend the use of indanedione in alcohol-free 
carriers because alcohols (methanol, ethanol, isopropanol) reduce the effective- 
ness of the reagent due to the formation of hemiketals. Roux et al., however, 



o 



xx vn 

Figure 5.16 The fluorescent product of the reaction between 1,2-indanedione 
and amino acid. (From Petrovskaia, O.G., Design and Synthesis of Chromogenic 
and Fluorogenic Reagents for Amino Acid Detection, Ph.D. thesis, University of 
Pennsylvania, Philadelphia, 1999.) 

used methanol in their best formulation and did not notice any adverse effect. 
As opposed to Joullie, 144 ’ 145 they did notice a positive effect of cooling the 
exhibits to liquid nitrogen temperature. 151 

Acetic acid was found to have a blurring effect on the developed prints 
and, hence, is not recommended for use in indanedione solutions. 150 After 
checking the various parameters, Wiesner et al. suggested a working solution 
composed of 1,2-indanedione (0.2%) in HFE7100 solvent, containing about 
7% ethyl acetate. 150 Preliminary observations indicate the following advan- 
tages of 1,2-indanedione over DFO: 

1. Higher sensitivity (it detects more identifiable prints) 

2. Higher solubility in nonpolar solvents 

3. Good results in a non-CFC solvent (HFE7100) 

4. Cost 

The reaction mechanism of 1,2-indanedione with amino acids was 
explored by Petrovskaia and Joullie, who suggest the formation of a 1,3-dipole 
(XXVII, Figure 5.16) as the fluorescent species. 112 

Wiesner et al. 150 report that no new prints can be observed in a sequential 
treatment with ninhydrin after 1,2-indanedione. In the authors’ opinion, this 
indicates a faster and more complete reaction of indanedione with amino 
acids than the DFO reaction with amino acids (after which ninhydrin does 
provide new prints). Thus, the use of indanedione may save one stage in the 
sequence: DFO, ninhydrin, PD, which can turn to indanedione and PD. 
Several groups in Germany, Switzerland, the United Kingdom, Canada, the 
United States, Australia, and Japan have initiated extensive studies to evaluate 
1,2-indanedione for operational use. The Israel Police, Division of Identifi- 
cation and Forensic Science (DIFS), has already begun to use 1,2-indanedione 
in casework involving serious crimes. 152 



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145. Hauze, D.B., Petrovskaia, O.G., Taylor, B., Joullie, M.M., Ramotowski, R., and 
Cantu, A.A., 1,2-Indanediones: new reagents for visualizing the amino acid 
components of latent prints, /. Forensic Sci., 43, 744, 1998. 

146. Almog, J., Springer, E., Wiesner, S., Frank, A., Khodzhaev, O., Lidor, R., Bahar, 
E., Varkony, H., Dayan, S., and Rozen, S., Latent fingerprint visualization by 

1.2- indanedione and related compounds: preliminary results, /. Forensic Sci., 
44, 114, 1999. 




147. Dayan, S., Almog, J., Khodzhaev, O., and Rozen, S., A novel synthesis of 
indanediones using the HOF.CH 3 CN complex,/. Org. Chem., 63, 2752, 1998. 

148. Cava, M.R, Little, R.L., and Napier, D.R., Condensed cyclobutane aromatic 
systems. V. The synthesis of some alpha-diazoindanones: ring contraction in 
the indane series, /. Am. Chem. Soc., 80, 2257, 1958. 

149. Wilkinson, D., Spectroscopic study of 1,2-indanedione, Forensic Sci. Int., 1 14, 
123, 2000. 

150. Wiesner, S., Optimization of the Indanedione Process for Fingerprint Devel- 
opment, M.Sc. thesis, (J.Almog and Y.Sasson, supervisors), Casali Institute 
of Applied Chemistry, The Flebrew University of Jerusalem, Israel, 2001. 

151. Roux, C., Jones, N., Lennard, C., and Stoilovic, M., Evaluation of 
1,2-indanedione for the detection of latent fingerprints on porous surfaces, 
/. Forensic Sci., 45, 761, 2000. 

152. Azoury, M. (Head, Latent Fingerprint Development Laboratory, Israel 
Police), personal communication, July 2000. 




Fingerprint Detection 
with Photoluminescent 
Nanoparticles 



6 



E. ROLAND MENZEL 



Contents 



The Essence of Time-Resolved Imaging 
Luminescence Lifetimes 
Basics of Time-Gated fingerprint Detection 
Basics of Phase-Resolved Imaging 
fingerprint Treatments 

Lanthanide-Based Procedures 
Photoluminescent Semiconductor Nanocomposites 
CdS Nanocrystals 
CdS/Dendrimer Nanocomposites 
Diimide Mediation of fingerprint Development with 
CdS/Dendrimer Nanocomposites 

Incorporation of Lanthanide Complexes into Dendrimers 
Cadmium Selenide Nanocrystals 
Ongoing Investigations 
References 



The exploitation of photoluminescence as a general approach to the detection 
of latent fingerprints began in 1976. 1 The rationale for the photoluminescence 
approach is the very high analytical sensitivity that photoluminescence tech- 
niques provide quite generally. One cannot do better than the detection of 
a single photon, a capability within reach in photoluminescence, fingerprint 
luminescence excitation initially used lasers, but filtered lamps (these days 
referred to as alternate or alternative light sources) were employed as well, 
albeit at the expense of detection sensitivity in comparison with lasers. This 
sensitivity discrepancy still pertains today. The initial fingerprint photolumi- 
nescence investigation focused on fluorescence inherent to fingerprint resi- 
due. However, the utilization of fluorescent dusting powders and staining 
dyes, as well as reagents that would attack fingerprint constituents to yield a 
fluorescent product, was also anticipated from the outset. By the late 1970s, 




Figure 6.1 Ninhydrin/ZnCl 2 vs. ninhydrin/InCl 3 fingerprint photoluminescence 
development. 

various fluorescent dusting powders had been developed. 2 Dye staining, first 
demonstrated in 1976, 1 came into its own in the early 1980s in concert with 
cyanoacrylate ester fuming. 3 This staining is today one of the most successful 
photoluminescence procedures for detection of fingerprints on smooth sur- 
faces, regardless of the age of the fingerprint. Numerous staining dyes can be 
employed. The post-treatment of ninhydrin-developed latent fingerprints by 
zinc chloride, first reported in 1982, 4 made fingerprints on porous items 
(mostly paper) tractable as well, and is today quite routine. Sensitivity 
improvements to this procedure, involving ninhydrin analogs, notably 
benzo(/)ninhydrin 5 and 5-methoxyninhydrin 6 followed. The zinc chloride 
post-treatment of ninhydrin-processed fingerprints was until very recently 
unsurpassed in terms of the intensity of the obtained photoluminescence. 
However, recent work carried out in Japan has identified indium chloride as 
being superior. 7 The InCl 3 is used in the same way as ZnCl 2 . Figure 6.1 depicts 
an example of the comparison of ZnCl 2 vs. InCl 3 treatment of a ninhydrin- 
processed fingerprint. More intense luminescence can be obtained with GaCl 3 
because Ga has a lower atomic number than In. However, GaCl 3 reacts fairly 
violently with water (which occurs in methanol that has been exposed to 
ambient air). Thus, GaCl 3 is not as practical as InCl 3 . Diazafluore-9-one is a 
relatively recent reagent that can be used instead of ninhydrin/zinc chloride. 8 
It is now routinely employed in a number of crime laboratories. With the 
above procedures, and a number of others for special situations, 9 photolu- 
minescence detection of fingerprints has assumed a prominent place world- 
wide as a major routine methodology. Photoluminescence detection of latent 



fingerprints has been instrumental in the solution of many major cases (e.g., 
Polly Klaas, Nightstalker). To the best of this author’s knowledge, laser detec- 
tion holds the record for the oldest fingerprint developed and identified in 
a criminal case over 40 years old. 10 In the author’s laboratory, ridge detail of 
fingerprints dating back to the American Civil War has been developed by 
laser. The photoluminescence approach has found use also in other crimi- 
nalistic applications, 9 such as document examination, fiber analysis, locating 
seminal fluid, and various instances of trace evidence detection. 11 The current 
state of the methodology has been dealt with extensively in journals as well 
as books, including the first edition of Advances in Fingerprint Technology. 12 
Thus, the focus in this second edition is on upcoming methodologies 
designed to permit detection of latent fingerprints on articles that display 
very intense background luminescence which masks the fingerprint lumines- 
cence obtained with the current procedures. This is a pervasive major prob- 
lem that still plagues the photoluminescence detection of fingerprints and, 
indeed, all photoluminescence-based analytical techniques. 



The Essence of Time-Resolved Imaging 

Whether in analytical chemistry, biotechnology, or criminalistics, the detec- 
tion of a weak photoluminescence in the presence of a strong background 
fluorescence is carried out following the same basic principles. They make 
use of the difference between the luminescence lifetimes of the background 
and analyte emissions. We begin by inquiring into the origin of this lifetime 
difference. 

Luminescence Lifetimes 9 

The emission of light by substances can have a number of causes, among 
them heat (incandescence) and chemical reaction (chemiluminescence), as 
in the luminol reaction with blood. For our purposes, the most important 
origin of luminescence, however, is the prior absorption of light (excitation) 
to give rise to photoluminescence. On the basis of luminescence lifetime (i.e., 
the decay time of the luminescence intensity once the excitation is cut off) 
two categories of photoluminescence were distinguished long before the 
quantum-mechanical underpinnings were understood; namely fluorescence 
of short lifetime and phosphorescence of long lifetime. The slowness concept 
distinguishing the two light emissions has evolved over time (toward shorter 
lifetimes of phosphorescence). The distinction between fluorescence and 
phosphorescence is placed on a less arbitrary footing when one examines the 
quantum-mechanical origin of the photoluminescence of typical organic 
molecules — which we are mostly concerned with in fingerprint work. For 




purposes of understanding their photoluminescence, these molecules can be 
thought of to good approximation as being two-electron systems. When the 
molecule is in the ground (unexcited) state, the two optically active electrons 
occupy the same molecular orbital, namely, the highest occupied molecular 
orbital (HOMO). Their spins must be antiparallel to satisfy the exclusion 
principle. The total spin (S) of the two electrons, namely the sum of the two 
spins (1/2 each), is thus zero and the spin multiplicity (2S + 1) is 1. The state 
is, accordingly, a singlet state. On optical excitation, one of the electrons is 
promoted to a molecular orbital of higher energy via the absorption of the 
excitation illumination, namely, to the lowest unoccupied molecular orbital 
(LUMO). The molecule is now in the excited state that gives rise to photo- 
luminescence. If no electron spin flip has taken place during the excitation 
process, the excited state is still a singlet state and the decay to the singlet 
ground state (i.e., electron jump back to HOMO), accompanied by emission of 
light, is termed fluorescence. If a spin flip has taken place, however, which is legal 
in terms of the exclusion principle because the two electrons no longer occupy 
the same orbital, the excited state becomes a triplet state (S = 1, 2S + 1 = 3) and 
the decay to the singlet ground state is termed phosphorescence. The distinc- 
tion between fluorescence and phosphorescence on the basis of electron spins 
is traced back to the nature of the electric dipole operator that describes the 
emission of light. It does not operate on spin. Thus, an allowed transition, 
namely one that can occur quickly, one that comes with a short lifetime, 
involves ground and excited states of the same spin multiplicity (2S + 1). 
When the spin multiplicities of the two states differ, the transition is forbid- 
den and thus does not occur quickly; hence, a long lifetime. This definition 
of fluorescence and phosphorescence is not universally followed. For exam- 
ple, the luminescences of lanthanides are often (sloppily) referred to as flu- 
orescences although the spin multiplicities of the involved states differ by 
even more than discussed above, and the lifetimes of lanthanide lumines- 
cences are very long compared to typical fluorescence lifetimes. Recombina- 
tion and trap luminescences, as found in semiconductor materials, are a 
different matter still. In this chapter we reserve the term “fluorescence” to 
the transition between molecular singlet states. Other transitions are referred 
to by the catch-all terms “luminescence” and “emission,” or are called “phos- 
phorescence” when appropriate according to the above-described criterion. 

Basics of Time-Gated Fingerprint Detection 

Suppose a latent fingerprint has been treated such that it phosphoresces and 
assume that it is located on a fluorescent article. Now illuminate the article 
with an appropriate laser (filtered lamps are generally not useful for time- 
resolved fingerprint detection) that is periodically turned on and off and 
assume there is on hand an imaging device that can be turned on and off 





^ ne- 



gate 

delay 

Figure 6.2 Time-gating scheme for time-resolved imaging to suppress back- 
ground fluorescence. 

synchronously with the laser. One then has the scheme depicted in Figure 6.2, 
in which the gate width denotes the time the imaging device is on and the 
gate delay represents the time interval between laser cut-off and imaging 
device turn-on. The delay is needed to ensure that the background fluores- 
cence has decayed by the time the imaging device becomes active. The imag- 
ing device turns off before onset of the next laser illumination cycle. The 
imaging device is typically a gateable CCD camera, namely a CCD camera 
equipped with a proximity-focused microchannel plate image intensifier. 9,13 
Figure 6.3 shows a typical block diagram of the pertinent imaging apparatus. 
The system depicted in the figure utilizes a mechanical light chopper, namely 
a rotating wheel with holes in it. This is appropriate when the fingerprint 
luminescence has a lifetime of millisecond order. The system in Figure 6.3 
calls for a laser of relatively high power, such as the Ar-laser typically 
employed in current routine fingerprint work. One can operate with much 
smaller lasers in systems in which fingerprints are scanned by a focused laser 
beam that is deflected by a pair of rotating mirrors, 14 in much the same way 
as the electron beam rastering in the acquisition of television images. Such 
systems tend to be slow, but have the virtue, apart from the small laser, of 
requiring only a cheap detector, such as a photomultiplier tube, instead of 
the expensive gateable CCD camera. For shorter lifetimes, which are beyond 
the capability of mechanical devices, an electro-optic light modulator or 
similar device would replace the light chopper. Now, however, optical align- 
ment and electrical biasing of the modulator make for difficulties as well as 



lens 




printer 



Figure 6.3 Block diagram of time-gated imaging apparatus. 

increased expense. For time-resolved imaging in such situations, a different 
approach is often taken. Time-gated imaging typically pertains to the domain 
of lifetimes longer than roughly 1 ps. 

Basics of Phase-Resolved Imaging 

Note that a fingerprint detection system based on the phase-resolved concept 
has yet to be developed. However, this is just a matter of time, given that 
phase-resolved imaging systems have been in operation for some time in 
applications such as cell microscopy. If one modulates the intensity of the 
illuminating laser light sinusoidally instead of on-off as in Figure 6.2, the 
thus excited luminescence is then also sinusoidal in intensity but is delayed 
with respect to the excitation by a phase that is related to the luminescence 
lifetime. There is also a related luminescence demodulation. The situation is 
shown in Figure 6.4, with normalized excitation and emission. (|)is the phase 
and m the demodulation. The effect of the angular modulation frequency CO, 
namely 2jtf (where f is the modulation frequency), on the phase and demod- 
ulation is depicted in Figure 6.5. Multiple luminescence lifetimes in phase- 
resolved spectroscopy and imaging can be distinguished by varying the mod- 
ulation frequency. Modulation frequencies of hundreds of megaHertz are 
readily obtainable. Thus, lifetimes of nanosecond order become accessible. 
It is only necessary that the analyte luminescence have a lifetime significantly 
different from that of the background for phase-resolved imaging to suppress 
the background. However, the fingerprint luminescence lifetime will gener- 
ally be longer in practise than that of the background because shortening of 
luminescence lifetime is generally attended by decrease in luminescence 
quantum yield (i.e., decrease in luminescence intensity). The desired finger- 
print luminescence lifetimes typically range from about 10 ns to about 1 ps 
(as compared to background fluorescence lifetimes of roughly 1 ns). A basic 




tan 4> = cox m = b/B = (1 + co 2 t 2 )' 1/2 

Figure 6.4 Phase shift and demodulation of luminescence vs. excitation (® = 
phase shift, co = modulation angular frequency, x = luminescence lifetime, m = 
demodulation). 




CO 

Figure 6.5 Phase and demodulation vs. modulation angular frequency. 

block diagram of the pertinent imaging apparatus is shown in Figure 6.6. 
More sophisticated versions are described elsewhere. 9 Here, one is primarily 
concerned with fingerprint treatments that yield luminescence lifetimes 
appropriate to the time-gated and phase-resolved domains, rather than the 
details of instrumentation. 




Figure 6.6 Block diagram of phase-shift/demodulation apparatus for time-resolved 
imaging. 



Fingerprint Treatments 

Fingerprint treatments suitable for time-resolved imaging began to be 
explored in the late 1980s. At first, transition metal complexes that yield 
charge-transfer phosphorescences were successfully examined and applied to 
fingerprint development by dusting or staining. 15 However, such complexes 
could not be utilized for chemical fingerprint development, thus limiting the 
approach primarily to smooth surfaces. Next, lanthanide-based procedures 
were explored. These have the potential of forming a universal photolumi- 
nescence approach to fingerprint detection, being applicable, in principle, to 
all types of surface and to fingerprints of any age. They have by now reached 
a reasonable level of maturity. However, problems persist with the lanthanide 
(rare earth) approaches, thus prompting more recent investigation of pho- 
toluminescent semiconductor nanocomposites. 

Lanthanide-Based Procedures 

The concept of time-resolved fingerprint detection for purposes of back- 
ground fluorescence suppression actually dates back to 1979. 16 Its feasibility 
then was explored using a rotating cylinder with slots cut into it to turn the 
laser illumination on and off. The photographic camera was placed such that 
the sample would come into its view at a time after laser cut-off, as shown 
in Figure 6.7. The arrangement resembles a phosphoroscope, a device that 
dates back to the 19th century. The sample was a fingerprint dusted with a 
powder that contained a Tb 3+ complex, yielding a green luminescence of 
millisecond-order lifetime. The fingerprint was located on yellow notepad 




photographic 

camera 



Figure 6.7 Phosphoroscope-like apparatus for time-resolved imaging. 

paper, which yields a very intense greenish yellow fluorescence. The feasibility 
of background elimination was demonstrated with the apparatus and sample. 
However, practicality was lacking, in the sense that the size of the rotating 
cylinder limits the size of the article to be examined, given that the article 
must fit inside the cylinder. The apparatus cannot be sufficiently scaled up 
in size for general purposes because of limitations in rotation speed of the 
cylinder, as well as decreased camera image resolution with increasing cylin- 
der size. The practicality issue was resolved in the early 1990s with a time- 
gated system as depicted in Figure 6.3. The corresponding fingerprint treat- 
ments at first involved lanthanide chemistries in which the zinc chloride post- 
ninhydrin step was replaced by a lanthanide halide (typically EuC 1 3 or 
TbCl 3 ). 17 Subsequently, lipid-specific chemistries were explored. 18 Dusting 
and staining procedures involving lanthanide complexes were developed in 
the early to mid-1990s. The various lanthanide procedures are detailed in 
Fingerprint Detection with Lasers, 2nd ed., revised and expanded. 9 The basic 
underpinnings of the lanthanide general strategy will thus only be briefly 
outlined. For chemical fingerprint processing, the general features of the 
involved lanthanide complexes are shown in Figure 6.8. The conjugating 
ligand serves to selectively bind to the fingerprint, and the complex of step 
1 in the figure is nonluminescent. The sensitizing ligand, attached subse- 
quently, produces the lanthanide luminescence by absorbing the excitation 



step 1 



step 2 



step 3 




Figure 6.8 Basic scheme for lanthanide-based chemical fingerprint development. 



light and transferring the excitation energy to the lanthanide ion by an energy 
transfer process akin to Forster intermolecular energy transfer. 9 For dusting 
and staining, the conjugating ligand is not needed. Figure 6.9 shows the 
energy-transfer scheme for europium complexes. 9 At the time of this writing, 
problems associated with chemical processing of fingerprints older than about 
1 week still persist. Furthermore, the excitation of lanthanide complexes 
demands ultraviolet (UV) light and thus is not compatible with many laser 
systems currently in use in fingerprint laboratories. An ultraviolet-capable 
argon-ion laser is a suitable excitation source. When time-resolved imaging 
is not mandatory — namely, when background fluorescence is not a 
problem — the fingerprint work can utilize an ordinary UV lamp. Explora- 
tion of fingerprint processing with photoluminescent semiconductor nano- 
particles as well as dendrimer application to fingerprint development were 
initiated about a year ago to remedy the above problems. These nanoparticle 
approaches are promising, especially in the time-resolved context, and are 
taken up in the remainder of this chapter. It is anticipated that they will form 
the next milestone in fingerprint detection methodology. 



Photoluminescent Semiconductor Nanocomposites 

Semiconductor materials such as CdS, CdSe, CdTe, InP, and InAs, which nor- 
mally are not luminescent, can become intensely luminescent when particles, 




5 



7 

7 
7 

F 3 + sensitizing 

ligand 

Figure 6.9 Ligand-to-europium energy transfer and europium luminescence 
energy-level diagram (waved arrows denote radiationless transitions and straight 
arrows radiative ones). 

typically in crystalline form, become very small (i.e., of nanometer order in 
size). Such nanoparticles can be quite robust. They are typically encapsulated 
with ZnS, silica, or organic material. This capping is sometimes referred to 
also as derivatization or functionalization, especially when an organic com- 
pound is involved, which is sometimes also referred to as a surfactant. The 
encapsulation amounts to covering the nanocrystal with a layer of material 
that may serve a variety of functions, for example, passivation to optimize 
luminescence efficiency, serving as a site for attachment of conjugating 
ligands designed for specificity of chemical binding, serving this labeling func- 
tion itself, serving to solubilize the nanocrystal, and preventing aggregation of 






nanocrystals. Photoluminescent semiconductor nanoparticles have recently 
become the subject of intense investigation in the biotechnology arena, 
mostly for labeling purposes. 19,20 DNA sequencing is an example. The salient 
virtues that distinguish the nanoparticles (referred to also as quantum dots, 
nanocrystals, and nanocomposites, depending on morphology) from ordi- 
nary fluorescent labels are that their absorption and luminescence wave- 
lengths (colors) can be tuned by varying the particle size and that the lumi- 
nescence lifetimes are long, ranging from roughly 10 8 to 10 6 s, thus making 
the nanoparticles suitable for time-resolved spectroscopy and time-resolved 
imaging, with flexibility in terms of useful laser light sources. These features 
are valuable from a biotechnology perspective and are, in principle, equally 
pertinent to the fingerprint context, thus prompting a study of their potential 
utility in fingerprint detection that commenced in 1999. 9 Because of financial 
and manpower constraints, this investigation has to date only aimed at reduc- 
tion to practice 21 (i.e., demonstration of feasibility rather than work-up of 
routine recipes). Nonetheless, a variety of nanoparticle systems and finger- 
print chemistries have been examined. Practical recipes will presumably fol- 
low once the best general approaches have been delineated. 

CdS Nanocrystals 22 

Photoluminescent semiconductor nanocrystals may be expected to be used 
for fingerprint detection in various ways, namely by incorporation into dust- 
ing powder in a manner akin to fluorescent dye blending with magnetic 
powder 9 by staining, especially once fingerprints have been exposed to 
cyanoacrylate ester; or by chemical bonding to constituents of fingerprint 
residue. In photoluminescence detection of fingerprints, the staining 
approach generally tends to be more effective when applicable to the article 
under examination, than dusting. Thus, the focus in this chapter section is 
on staining with CdS nanocrystals. As a preface to this mode of fingerprint 
detection, the photophysical properties of CdS quantum dots are examined, 
primarily to assess suitability for phase-resolved imaging to suppress back- 
ground fluorescence, but also to determine suitable excitation wavelengths. 

The employed CdS nanocrystal samples, prepared in inverse micelles 23,24 
and capped with dioctyl sulfosuccinate (sodium salt), were obtained from 
Professor John T. McDevitt (Chemistry Department, University of Texas, 
Austin). Solubilization of the nanocrystals utilized heptane or a mixture of 
hexanes (CH 3 C 4 H 8 CH 3 ). Solutions had quantum dot concentrations of mil- 
ligram/milliliter order. Absorption spectra in these solvents exhibited band 
edges at about 440 nm and very broad absorbance (with some structure, but 
not absorption peaks as in typical atomic or molecular spectra) that increased 
with decreasing wavelength to 300 nm, the lowest wavelength in our absorp- 
tion measurements. The spectra, fairly typical of semiconductor absorption 





Wavelength (nm) 



Figure 6.10 Absorption spectra of CdS nanocrystals in hexane (solid line) and 
heptane (dashed line). 

spectra, are shown in Figure 6.10. They serve to determine the sizes of the 
nanocrystals, 23 which were deduced to have radii of 3 to 4 nm. The nano- 
crystal luminescence (band width about 100 nm) peaked at about 580 nm, 
with a second, weaker luminescence band in the 400 to 450-nm range. In 
terms of intensities as a function of excitation power, excitation wavelength, 
solvent system, etc., the luminescence spectroscopy of nanocrystals tends to 
be more complex than that of typical fluorescent molecules because in nano- 
crystals one likely has a number of different, and quite variable, trap states 
that contribute to the luminescence, including surface traps, as well as the 
intrinsic semiconductor recombination process. Thus, the spectroscopic fea- 
tures generally need to be examined for the samples at hand, with literature 
results serving as approximate guides only. Lifetime measurements for hep- 
tane solution used phase-shift/ demodulation techniques, as described earlier, 
and employed a HeCd laser (operating at 325 nm). The lifetime measurement 
corresponded to the total luminescence (transmitted to the detector through 
a long-wavelength-pass filter). Laser modulation frequencies ranged from 0.1 
to 100 MHz. The fit to the obtained phase shift and demodulation curves, 
analogs to the curves shown in Figure 6.5, yielded three lifetime components. 
Approximately 70% of the luminescence intensity corresponded to emission 
with lifetime of about 1000 ns, about 25% to emission with lifetime of about 
70 ns, and about 5% to emission with lifetime of 0.54 ns. This latter is excitonic 
emission and the obtained lifetime is in good agreement with the literature. 25 
Total luminescence lifetime measurement was made, rather than lifetime mea- 
surement at a particular wavelength or a set of particular wavelengths, because 
fingerprint luminescence imaging usually involves the total luminescence. 




Figure 6.11 Photoluminescence of fingerprint on soft drink can fumed with cyano- 
acrylate ester and subsequently stained with CdS nanocrystal heptane solution. 

Because staining with fluorescent dye after cyanoacrylate ester fuming is 
a very successful fingerprint detection methodology, we employed the above 
dioctyl sulfosuccinate-capped CdS nanocrystals, dissolved in heptane or hex- 
ane, in this manner. Sample fingerprints were placed on a soft drink can 
(Coca Cola®) and on aluminum foil, and were fumed with cyanoacrylate 
ester. The samples were then immersed in the nanocrystal solutions for times 
ranging from a few seconds to a few minutes. Immersion times were not 
critical. The samples were then left to dry. Luminescence examination under 
an Ar-laser operating in the near-UV (a good excitation regime) revealed 
amply intense luminescence. Because there was a generally heavy coverage 
of the immersed sample portion masking fingerprint detail, samples were 
subjected to gentle rinsing with hexane to remove excess nanocrystal depo- 
sition, leaving behind fingerprint detail. An example is shown in Figure 6.11. 
This photograph and all others below were taken with a digital camera 
(Kodak DC 120) equipped with a close-up lens. Because background fluo- 
rescence was not an issue with the utilized samples, it was not necessary to 
perform time-gated or phase-resolved imaging. 

Any preferential adherence of the organically capped CdS nanocrystals 
to unfumed fingerprints would involve nonpolar fingerprint constituents, 
such as lipids, and these readily dissolve in hexane or heptane (particularly 
the former, which is more agressive than the latter because of lower viscosity). 
Thus, unfumed fingerprints on metal, plastic, glass, etc. could not be devel- 
oped by the above staining. However, on black electrical tape (sticky side), 
unfumed fingerprints could be stained successfully with heptane nanocrystal 
solution and with heptane rinsing. General optimization work in terms of 
solvent delivery systems is called for. 



CdS/Dendrimer Nan ocom posi tes 26 2 7 

Dendrimers — polymers of tree-like structure — have lately begun to com- 
mand intense attention 28 in many areas of science, especially in connection 
with their incorporation with nanoparticles of various kinds for purposes of 
applications that include cancer drug delivery, catalysis, waste clean-up, opti- 
cal devices, etc. Of particular interest here is a photoluminescent nanocom- 
posite of CdS with Starburst® (PAMAM) dendrimer that was first (outside 
the forensic science arena) described by Sooklal, Hanus, Ploehn, and Mur- 
phy. 29 The nanocomposite contains nanoparticle-size clusters of CdS that are 
incorporated into aggregates of dendrimer molecules. The Starburst® den- 
drimers are of particular interest from our perspective because they are 
commercially available (Aldrich), a must for any practical utilization in fin- 
gerprint laboratories. These dendrimers come with either amino or carbox- 
ylate terminal functional groups, which are useful for chemical fingerprint 
processing. Depending on size, amino-functionalized Starburst® (PAMAM) 
dendrimers are referred to as generation 0, 1, 2, 3, 4, ... They have, respec- 
tively, 4, 8, 16, 32, 64, ... terminal amino groups. Similarly, generation -0.5, 

0. 5, 1.5, 2.5, 3.5, . . . have, respectively, 4, 8, 16, 32, 64, . . . terminal carboxylate 
(sodium salt) groups. The first three generations of each type are shown in 
Figures 6.12 and 6.13. 

The initial CdS/ dendrimer nanocomposite study involved generation 0, 

1, and 4 dendrimer (4, 8, 64 amino terminal groups, respectively). As pur- 
chased, the dendrimers come in methanol solution. The preparation in meth- 
anol of the CdS/dendrimer nanocomposite simply involves diluting the 
dendrimer solution and adding to it small quantities (aliquots) of equimolar 
methanol solutions, in equal volumes, of cadmium nitrate and of sodium 
sulfide. In the absence of dendrimer, the reaction of the cadmium nitrate 
and sodium sulfide would produce the cadmium sulfide as a precipitate in 
large clumps. In the presence of dendrimer, however, an aggregate of CdS of 
nanoparticle size with the dendrimer is formed, as is depicted in Figure 6.14. 
The aliquots of cadmium nitrate and sodium sulfide may be added to the 
dendrimer solution simultaneously or sequentially in either order. In our 
experiments, either five or ten aliquots of each reagent were used to produce 
the desired nanocomposite, with concentrations as described shortly. In addi- 
tion to the methanol formulation of the CdS/dendrimer nanocomposite, a 
10% methanol: 90% water formulation was also investigated. The nanocom- 
posite preparation utilized 1:9 methanokwater solutions of the dendrimer, 
cadmium nitrate, and sodium sulfide instead of pure methanol solutions, 
but was otherwise conducted the same way. The rationale for the 1:9 meth- 
anokwater solvent system was simply the general desirability of water-based 
chemistry. The methanol served for initial dissolution of reagents and was 
then added to the water. 



H O 



H 



l-K 
H \ 
H' 



N— CH 2 CH 2 — N — C — CH2CH2 ^ ^CH 2 CH 2 CONHCH2CH 2 NH2 

. nch 2 — ch 2 i\l 

N— CH2CH2— N — C— CH 2 CH 2 / ^ CH2CH2CONHCH2CH2NH2 



O 



Generation 0 



NH2CH2CH2NHCOCH2CH2 



NCH2CH2NHCOCH2CH2 



' nch 2 — ch 2 n 



/ 



Generation 1 



NH2CH2CH2NHCOCH2CH2 

^ NCH2CH2NHCOCH2CH2 

/ \ 



NCH2CH2NHCOCH2CH2 



\ 

I 

./ 



,nch 2 — 



Generation 2 

Figure 6.12 Chemical structures of NH 2 functionalized Starburst® (PAMAM) 
dendrimers. 

For physical fingerprint treatments akin to dye staining, fingerprints 
(fresh to 1 -day-old) were placed on aluminum foil and Ziploc® (polyethylene) 
sandwich bags. Some of the samples were fumed with cyanoacrylate ester 
before staining with the nanocomposite, while other fingerprints were stained 
without the pre-fuming. With nanocomposites in methanol, the best results 
were invariably obtained, regardless of concentrations, when the nanocom- 
posites involved the generation 4 dendrimer rather than generation 0 or 1. 
Thus, this dendrimer is the focus of the discussion that follows. With den- 
drimer concentration greater than about 1 0 4 M, solutions were quite tacky 
and produced too much background via indiscriminate adherence to the 




sample, rather than preferential adherence to the fingerprint on the sample. 
Thus, the dendrimer concentrations employed ranged from 2 to 8 x 10 ~ 5 M 
in methanol as well as 1:9 methanohwater preparations. In methanol solu- 
tion, the observed luminescence was blue-green regardless of CdS concen- 
tration in the nanocomposite and increased with the CdS concentration. For 
2 x 10 -5 M dendrimer concentration, the nanocomposite precipitated out 
essentially immediately when the CdS concentration exceeded about 2 x 10 -3 M. 
An optimal CdS/dendrimer (generation 4) concentration of 8 x 10 '72 x 1 O ’ M 
produced solutions stable for several days at least, at room temperature. The 
situation was rather different for the 1:9 methanohwater case. Here, the 
luminescence color was generally yellow-orange and optimal CdS/dendrimer 
(generation 4) concentration was 2 x 10^78 x 10~ 5 M. Unlike in methanol, 
no nanocomposites could be formed with generation 0 and 1 dendrimer in 
1:9 methanohwater because of immediate precipitation. That luminescence 
colors were invariant with concentrations, in methanol and also in 1:9 meth- 
anohwater, indicates that the CdS nanocluster sizes are invariant, with nan- 
ocluster concentrations in the aggregates with generation 4 dendrimer 
varying. The optimizations cited above were assessed on the basis of lumi- 
nescence intensity in solution as well as in fingerprint development, with 
solution stability demanded as well. 

Absorption spectra of CdS/generation 4 dendrimer solutions in metha- 
nol and 1:9 methanohwater were shape-wise similar to the CdS nanocrystal 
spectra shown in Figure 6.10. A comparison with literature spectra 23 indi- 
cated CdS nanocluster sizes of about 2.5 and 3 nm, respectively. Lumines- 
cence excitation spectra yielded intensity drop-off at wavelengths longer than 
about 360 and 390 nm, respectively, in agreement with the absorption band 
edges. That the luminescence color in the methanohwater case is nonetheless 
orange, that is, unusually far red-shifted (in comparison with the blue-green 
luminescence in the methanol case), suggests the presence of Forster-type 
energy transfer 9 in the methanohwater system. As in the CdS nanocrystal 
case, luminescence lifetime measurements by phase-shift/demodulation 
techniques were best interpreted by three component fits. In the methanol 
case, the main component, with intensity fraction of about 0.6, had a 120-ns 
lifetime. The next component, with about 0.3 intensity fraction, had a 30-ns 
lifetime. The third component had a 3.5-ns lifetime. In the methanohwater 
case, the longest-lived component had a 300-ns lifetime and an intensity 
fraction of about 0.35. The next component, with 60-ns lifetime, had an inten- 
sity fraction of about 0.45. The shortest-lived component had a luminescence 
lifetime of about 4.5 ns. The lifetime data were reproducible over a range of 
CdS/dendrimer concentrations in both the methanol and methanohwater solu- 
tion systems. Solution emission spectra showed broad luminescences of 1 00 nm 




Figure 6.15 Photoluminescence of fingerprint on polyethylene fumed with 
cyanoacrylate ester and subsequently stained with CdS/generation 4 dendrimer 
methanol solution. 

full-width at half-maximum peaked at about 480 nm in methanol and 
130 nm fwhm peaked at about 550 nm in 1:9 methanokwater. 

Fingerprint staining with the methanol and methanokwater formula- 
tions simply involved dipping the aluminum foil and polyethylene samples 
and then letting them dry completely. In the customary staining with fluo- 
rescent dyes such as rhodamine 6G, the article is immersed for no more than 
a few seconds or is sprayed with the dye solution. In the CdS/dendrimer 
nanocomposite case, however, the immersion involved not seconds, but 
hours. Methanol solution dipping was not successful with unfumed finger- 
prints because the agressive methanol tended to dissolve away the fingerprint. 
Cyanoacrylate ester pre-fumed fingerprints, on the other hand, developed 
readily on both aluminum foil and polyethylene. An example is shown in 
Figure 6.15. The luminescence excitation was at 50 mW, near-UV, from an 
Ar-laser. The methanokwater CdS/dendrimer solutions lent themselves to 
fumed as well as unfumed fingerprints on the aluminum foil and polyethyl- 
ene samples. Dipped articles were typically left overnight in the solution 
before luminescence examination. Development of unfumed fingerprints on 
paper was attempted but was not successful because of excessive adherence 
of the nanocomposites everywhere on the paper. The long immersion times 
required for fingerprint processing suggest that a chemical reaction of the 
amino functionality of the dendrimer with carboxylic acid (or ester) of the 
fingerprint, or, for that matter, perhaps with the cyanoacrylate ester func- 
tionality, is involved, rather than physical preferential deposition, as in the 
staining with dye such as rhodamine 6G. The chemistry would be an ami- 
dation, as shown in Figure 6.16. This corresponds to a chemical labeling 
strategy widely used in biotechnology. 



o 



o 



R— C— OH + R' NH 2 



R — C — N — R' + H 2 0 
H 



Figure 6.16 General scheme of amidation reaction. 



Diimide Mediation of Fingerprint Development 
with CdS/Dendrimer Nanocomposites 27 

The amidation of Figure 6.16 could, in principle, involve the reaction of 
generation 4 dendrimer (amino -terminal functional groups) with fatty acids 
of fingerprint residue or the reaction of generation 3.5 dendrimer (carbox- 
ylate-terminal functional groups) with amino acids or proteins of fingerprint 
material. Both prospects were investigated. In either case, the direct reaction 
as depicted in Figure 6.16 is likely not very efficient because the involved OH 
group of the carboxylic acid is a poor leaving group (i.e., one difficult to 
displace). A remedy that has been reported in the biochemistry literature 20 
and that is fairly commonly used in that field involves the mediation of the 
amidation by a carbodiimide, as is shown in the reaction scheme of 
Figure 6.17. For this purpose, the most widely used carbodiimide is dicyclo- 
hexylcarbodiimide. However, it dissolves in nonpolar solvents, which are not 
very well-suited for fingerprint work. Indeed, dissolving the diimide in 
dichloromethane caused (lipid components of) fingerprints to be dissolved. 
However, the problem can be remedied by employing a carbodiimide soluble 
in water, namely l-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochlo- 
ride, whose structure is shown in Figure 6.18. Initially, the 1:9 methanol:water 
solvent system was chosen for the diimide, with fingerprints on aluminum foil 
(no background due to indiscriminate adherence of CdS/dendrimer, as with 
paper) immersed in the diimide solution prior to exposure to the nanocom- 
posite. However, prolonged immersion in this diimide solution resulted in 
chemical attack on the aluminum foil itself, producing a tarnished appear- 
ance of the foil. Thus, the methanol was deleted. A standard solution of 2.5% 
(by weight) diimide in water served for fingerprint pretreatment. Finger- 
prints immersed in pure water for the same time served as controls. Subse- 
quent fingerprint processing by CdS/ generation 4 dendrimer used 2 x 10 4 /8 
X 1 0 5 M nanocomposite formulation in 1:9 methanokwater. Diimide pre- 
treatment for times of about 1 hr or less produced no enhancement in fin- 
gerprint development compared to the water controls. However, with time 
spans between about 5 and 24 hr, significant enhancement was observed, 
with the enhancement leveling off by 24 hr. These observations are indicative 



R — C OH + R' — N = C=N — R" p 

O NHR" 

II I 

R C— O— C=NR' + R"' NH 2 =^= 

Q . NHR" 

r l> I , 

— — L R C O— C=NHR' J 

NHR"' 



NHR" 

0 I 

II I 

R C— O— C=NR' 

OH NHR" 

r 1 1 
R C— O— C=NR' I 

I 

NHR'" 

► R'NHCNHR" + 



R C N R'" 



Figure 6.17 Carbodiimide-mediated amidation reaction. 



CH 2 

\ N (CH 2 ) 3 N = C = N CH 2 CH 3 HCI 

CH 2 ^ 

Figure 6.18 Structure of 1 -(3-dim ethylaminopropyl)-3-ethylcarbodiimide hydro- 
chloride. 

of chemical fingerprint labeling. Results with polyethylene, paper, and 
cyanoacrylate ester-fumed fingerprints suggest an additional contribution by 
preferential physical adherence of the nanocomposite to fingerprint material. 
In general, chemical reaction rates increase with increasing temperature. 
Accordingly, the diimide pretreatment was examined at 60°C in comparison 
with room temperature. At the elevated temperature, severe chemical attack 
on the aluminum foil substrate of samples occurred for heating times longer 
than about 1 hr. For shorter heating times, no fingerprint development 
enhancement was observed. If there is chemical binding of the generation 4 
nanocomposite to fingerprint constituents in the absence of diimide, one 
might expect an enhancement of fingerprint development with temperature 
upon direct application of the CdS/dendrimer solution. Such enhancement 
was indeed observed. 




The amidation reaction depicted in Figure 6.16 should, in principle, 
occur when carboxylate-functionalized dendrimer reacts with amino acid or 
protein of fingerprint residue. Thus, we examined CdS/generation 3.5 den- 
drimer utility for fingerprint development. The choice of generation 3.5 
dendrimer was made to permit direct comparison with generation 4 den- 
drimer, both generations having 64 terminal functional groups. The prepa- 
ration of the nanocomposite was as described earlier, with methanol as well 
as 1:9 methanohwater (2 x 10 '78 x 1 0 5 M concentration) solvent systems. 
As before, methanol solutions were ineffective on unfumed prints, which 
tended to be dissolved away. Staining of cyanoacrylate ester fumed prints 
yielded results very similar to those encountered with nanocomposites based 
on generation 4 dendrimer, with no advantage derived from the use of the 
generation 3.5 dendrimer. In contrast with what was observed with genera- 
tion 4 dendrimer use, the 1:9 methanohwater formulation of the generation 
3.5 nanocomposite produced no fingerprint development whatsoever for 
unfumed fingerprints on aluminum foil or polyethylene at room temperature 
and in the absence of carbodiimide. This might not be entirely surprising in 
that different constituents of the fingerprint are probed in the two cases and 
because the amino acid of the fingerprint might be buried beneath lipids in 
lipid-rich fingerprints, which pertained to our study (fingerprints rubbed on 
the forehead prior to deposition). This would be aggravated by the inherent 
incompatibility of the polar solvent system with lipids. However, one should 
realize that a certain level of incompatibility between fingerprint and reagent 
solvent system is mandatory to ensure that the fingerprint not be dissolved. 
The situation is reminiscent of what is encountered in lipid fingerprint devel- 
opment with lanthanide chelates. 18 There, the addition of a small amount of 
acetone to the solvent system served to solubilize fingerprint lipids just 
enough for reaction. This was not successful with the generation 3.5 nano- 
composite, but crisp luminescent fingerprint detail was obtained with the 
generation 4 nanocomposite. This suggests that solubility issues are not 
responsible for the failure of fingerprint development with the generation 
3.5 nanocomposite formulation. Accordingly, we next examined the prospect 
of pretreatment of the generation 3.5 dendrimer with diimide prior to expo- 
sure of fingerprints to the dendrimer. The successful sequence involved first 
mixing in stoichiometric amounts the diimide with the generation 3.5 den- 
drimer, keeping in mind that the latter has 64 functional terminal groups, 
in 1:9 methanohwater. The mixture was then heated overnight at 60°C. CdS 
was subsequently incorporated by aliquot addition, as described earlier, and 
fingerprint samples were finally immersed in the solution. Figure 6.19 shows 
a fingerprint developed via this treatment sequence. The fingerprint lumi- 
nescence was orange. The stoichiometric addition of diimide (about 1.5 x 




Figure 6.19 Photoluminescence of fingerprint (on aluminum foil) developed by 
diimide-mediated CdS/generation 3.5 dendrimer treatment (see text). 

1 0 2 M diimide to 2.4 x 1 0 4 M dendrimer) was intended to minimize the 
formation of ester in the fingerprint residue itself upon subsequent sample 
immersion. The ester formed would tie up the amino acid of the fingerprint 
that otherwise would react with dendrimer. The heating step was essential. 
Without it, fingerprint development was only faint. The diimide reacts with 
aluminum foil to give it a tarnished appearance, much like tarnished silver. 
Without the heating step, this tarnishing resulted upon immersion of alumi- 
num foil samples. One can thus presume that the counterproductive reaction 
with fatty acid of the fingerprint residue also occurs. With heating, on the 
other hand, no foil tarnishing was seen, indicating that the diimide had been 
tied up by the dendrimer, as desired. Formation of the CdS/dendrimer nano- 
composite followed by diimide addition (prior to fingerprint sample immer- 
sion) was not successful, perhaps because of excessive aggregation prior to 
the addition of the diimide. Although the above-described fingerprint label- 
ing by dendrimer, as mediated by carbodiimide, has only been explored for 
feasibility to date, rather than having reached the practical recipe stage, a 
reasonable grasp of the underlying chemistry has hopefully emerged. 

Incorporation of Lanthanide Complexes into Dendrimers 21 

Because dendrimers have many voids (of varying sizes), one can envision 
intercalation of molecules in the dendrimer (i.e., their placement into voids 




Figure 6.20 Photoluminescence of fingerprint on aluminum foil developed by 
diimide-mediated treatment with europium complex/generation 3.5 dendrimer. 

of the dendrimer) in much the same way in which catalysts and cancer drugs 
are envisioned to be incorporated into dendrimers, as depicted in Figure 6.14. 
Preliminary work indicates that this is feasible, as shown in Figure 6.20. The 
europium complex with thenoyltrifluoroacetone, 9 generation 3.5 Starburst® 
(PAMAM) dendrimer, 1:9 methanokwater solvent system, carbodiimide, and 
sample (fingerprint on aluminum foil) immersion for 24 hr were involved. 
A control sample processed similarly, but in the absence of the dendrimer, 
failed to produce comparable fingerprint development (red luminescence 
under near-UV excitation). 

Cadmium Selenide Nanocrystals 30 

The fabrication of cadmium selenide nanocrystals involves high-temperature 
chemistry that must be performed under an inert (Ar) atmosphere — which 
comes with considerable difficulty and hazard. At present, these nanocrystals 
are not commercially available, except perhaps in research (milligram) sample 
quantity (at high price). However, companies are forming at this time, such 
that one can anticipate that a range of CdSe nanocrystals will become com- 
mercially available in the near future. CdSe quantum dots are typically encap- 
sulated with zinc sulfide. The encapsulant, quite apart from its protective 
function, serves as substrate for the attachment of conjugating ligands that 
are designed to selectively label substances of interest. The structure of encap- 
sulated and functionalized nanocrystals is depicted in Figure 6.21. The work 
done to date on thus functionalized quantum dots has primarily targeted the 





Figure 6.21 Structure of encapsulated and functionalized CdSe nanocrystal. 

biotechnology arena, and the functionalization has tended to involve carbox- 
ylate and amino groups. Given the above-described dendrimer investigation, 
we have in place a chemistry that should lend itself to the fingerprint context. 
Because of the high cost and low availability of CdSe nanocrystals, we have to 
date only addressed fingerprint development with carboxylate-functionalized 
ones (obtained from Quantum Dot Corp., Palo Alto, CA). Diimide mediation 
of the chemical fingerprint labeling was essential (fingerprints 1 -month-old on 
aluminum foil). Heating was not useful, destroying the nanocrystals. Nano- 
crystals are generally stored at low temperature (about 4°C) to prevent floccu- 
lation. No fingerprint development was obtained at that temperature, even with 
sample immersion for up to 5 days. At room temperature, 24-hr fingerprint 
immersion in a water solution containing in 1 p M concentration the water- 
soluble CdSe/ZnS/carboxylate functionalized nanocrystals and in 8 p M concen- 
tration the water-soluble l-(3-dimethylaminopropyl)-3-ethylcarbodiimide 
hydrochloride produced development of luminescent fingerprints. An example 
is shown in Figure 6.22. The carbodiimide relative concentration was kept low 
(one would normally use higher concentration) to prevent flocculation of 
nanocrystals. The low nanocrystal concentration itself was dictated by the 
limited nanocrystal supply. 

In keeping with semiconductor characteristics (i.e., broad band-structure 
characteristics in absorption), the utilized nanocrystals luminesced under 
excitation that could range from the ultraviolet to the red. This makes for 
greater flexibility in terms of the excitation light source. The comparatively 
rather sharp red luminescence peaked at 635 nm and had full-width at half- 
maximum of 35 nm (comparable to molecular fluorescence); the absorp- 
tion/luminescence spectra are shown in Figure 6.23. Luminescence lifetime 
measurements were best interpreted by two-component fits. These yielded 




Figure 6.22 Photoluminescence of fingerprint on aluminum foil developed by 
diimide-mediated treatment with ZnS-encapsulated and carboxylate-functional- 
ized CdSe nanocrystal water solution. 




wavelength (nm) 



Figure 6.23 CdSe nanocrystal absorption and luminescence spectra. 




components of about equal intensity fractions and lifetimes of 3 and 9.5 ns 
for carboxylate functionalized nanocrystals and of 6 and 24 ns for amino- 
functionalized ones. Note that nanocrystal sizes can be tailored to produce 
luminescence ranging from blue to red. Typically, luminescence lifetimes 
would increase as the emission blue-shifts. We chose red-emitting nanocrys- 
tals for study to maximize excitation flexibility. 

Ongoing Investigations 

From the work on nanocrystals and naocomposites done to date, as described 
above and including the utilization of dendrimers and the functionalizations 
with carboxylate and amino groups, it would appear that a fair understanding 
of the involved chemistry is at hand and that this is a chemistry that poten- 
tially offers much flexibility in fingerprint processing. Thus, current work is 
beginning to tackle the formulation of recipes of practicality. In particular, 
our aim is to devise procedures for porous surfaces, especially papers, which 
thus far remain elusive. Furthermore, work is in progress to optimize stain- 
ing-type approaches in concert with cyanoacrylate ester-fumed fingerprints. 
In addition to the utilization of nanocrystals and nanocomposites, we are 
expanding the exploration of the incorporation of lanthanide complexes into 
dendrimers. The driving force behind this direction is the fact that the very 
long lanthanide luminescence lifetimes permit time-resolved imaging by 
time-gated techniques, which are simpler than the phase-resolved counter- 
parts. The diimide-mediated amidation reaction that forms the core of the 
chemical fingerprint development described in this chapter involves an inter- 
mediate O-acylurea derivative of the carbodiimide that is reported to be 
unstable. Instead of nucleophilic attack by the primary nitrogen of the amino 
compound to form the amide, it may undergo hydrolysis, regenerating the 
starting carboxylic acid and producing a urea derivative of the carbodiimide. 
To assist the amidation reaction, N-hydroxysuccinimide has been reported 
in biochemical application. 31 The compound produces a stable active ester 
that then reacts with the amino compound to yield the amide. We are cur- 
rently exploring the application of this approach, as shown in the reaction 
scheme of Figure 6.24, to fingerprint development. While the biochemistry 
literature may at times be a good guide to chemistries applicable to the 
fingerprint context, it is worthwhile to reiterate that there is a major difference 
between the two fields in that in chemistry one generally wants reagent and 
analyte to be soluble in the same solvent, whereas in the fingerprint situation 
one must have incompatibility of the fingerprint and the reagent. Otherwise, 
fingerprint detail will bleed, at best — or be obliterated altogether. 



o 



o 



o 




Figure 6.24 Carbodiimide- and N-hydroxysuccinimide-assisted amidation. 



References 

1. Dalrymple, B.E., Duff, J.M., and Menzel, E.R., Inherent fingerprint 
luminescence — detection by laser, /. Forensic Sci., 22, 106-115, 1977. 

2. Menzel, E.R., Fingerprint Detection with Lasers, New York: Marcel Dekker, 1980. 

3. Menzel, E.R., Burt, J.A., Sinor, T.W., Tubach-Ley, W.B., and Jordan, K.J., Laser 
detection of latent fingerprints: treatment with glue containing cyanoacrylate 
ester, /. Forensic Sci., 28, 307-317, 1983. 

4. Herod, D.W. and Menzel, E.R., Laser detection of latent fingerprints: ninhy- 
drin followed by zinc chloride, /. Forensic Sci., 27, 513-518, 1982. 

5. Menzel, E.R. and Almog, J., Latent fingerprint development by frequency- 
doubled neodymium:yttrium aluminum garnet (Nd:YAG) laser: 
benzo(f)ninhydrin. /. Forensic Sci., 30, 371-382, 1985. 

6. Almog, J. and Hirshfeld, A., 5-Methoxyninhydrin: a reagent for the chemical 
development of latent fingerprints that is compatible with the copper- vapor 
laser./. Forensic Sci., 33, 1027-1030, 1988. 

7. Takatsu, M., (National Police Agency, Japan), personal communication, 1999. 

8. Pounds, C.A., Grigg, R., and Monkolaussavaratana, T., The Use of 1,8-Diaz- 
afluoren-9-one (DFO) for the Fluorescent Detection of Latent Fingerprints 
on Paper, Report No. 669, Central Research and Support Establishment, 
Home Office Forensic Science Service, Aldermaston, U.K., 1989. 

9. Menzel, E.R., Fingerprint Detection with Lasers, 2nd ed., revised and 
expanded, New York: Marcel Dekker, 1999. 

10. Starnes, N.S., Interesting case, Identification News, 34(10), 13, 1984. 

11. Creer, K.E., The detection and photography of fluorescent marks, in Fluores- 
cence Detection, Menzel, E.R., Ed., Proc. SPIE, 743, 175-179, 1987. 

12. Lee, H.C. and Gaensslen, R.E., Eds. Advances in fingerprint technology, New 
York: Elsevier, 1991. 




13. Murdock, R.H. and Menzel, E.R., A computer interfaced time-resolved imag- 
ing system, /. Forensic Sci., 38, 521-529, 1993. 

14. Roorda, R.D., Ribes, A.C., Damaskinos, S., Dixon, A.E., and Menzel, E.R., A 
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Forensic Sci., 45, 563-567, 2000. 

15. For example: Menzel, E.R., Laser detection of latent fingerprints: tris(2,2'- 
bipyridyl)ruthenium(II) chloride hexahydrate as a staining dye for time- 
resolved imaging, in Fluorescence Detection II, Menzel, E.R., Ed., Proc. SPIE, 
910, 45-51, 1988. 

16. Menzel, E.R., Laser detection of latent fingerprints — treatment with phos- 
phorescers. /. Forensic Sci., 24, 582-585, 1979. 

17. For example: Menzel, E.R., Detection of latent fingerprints by laser-excited 
luminescence, Anal. Chem., 61, 557A-561A, 1989. 

18. For example: Allred, C.E. and Menzel, E.R., A novel europium-bioconjugate 
method for latent fingerprint detection, Forensic Sci. Int., 85, 83-94, 1997. 

19. Bruchez, Jr., M., Moronne, M., Gin, P., Weiss, S., and Alivisatos, A.R, Semi- 
conductor nanocrystals as fluorescent biological labels, Science, 281, 
2013-2016, 1998. 

20. Chan, W.C.W. and Nie, S., Quantum dot bioconjugates for ultrasensitive 
nonisotopic detection, Science, 281, 2016-2018, 1998. 

2 1 . Menzel, E.R., Fingerprint Development Methods, U.S. Patent application No. 
09/487,702 (2000). 

22. Menzel, E.R., Savoy, S.M., Ulvick, S.J., Cheng, K.H., Murdock, R.H., and 
Sudduth, M.R., Photoluminescent semiconductor nanocrystals for finger- 
print detection, /. Forensic Sci., 45, 545-551, 2000. 

23. Ogawa, S., Fan, F.F., and Bard, A.J., Scanning tunneling microscopy, tunneling 
spectroscopy, and photoelectrochemistry of a him of Q-CdS particles incor- 
porated in a self-assembled monolayer on a gold surface, /. Phys. Chem., 99, 
11182-11189, 1995. 

24. Steigerwald, M.L., Alivisatos, A.P., Gibson, J.M., Harris, T.D., Kortan, R., and 
Muller, A.J., Surface derivatization of semiconductor cluster molecules,/. Am. 
Chem. Soc., 110, 3046-3050, 1998. 

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26. Menzel, E.R., Takatsu, M., Murdock, R.H., Bouldin, K.K., and Cheng, K.H., 
Photoluminescent CdS/dendrimer nanocomposites for fingerprint detection, 
/. Forensic Sci., 45, 758-761, 2000. 

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Silver Physical Development 
of Latent Prints 




ANTONIO A. CANTU 
JAMES L. JOHNSON 



Contents 



Introduction 
Background 
Carrier Solvents 

The Silver Physical Development Process 

Silver Physical Development in Photographic Chemistry 
The Photographic Developers 
Development Centers 
Fixation 
Comments 

The Silver Physical Development Process of Latent Prints 
on Porous Surfaces 

Mechanism of Silver Physical Development 
Electrochemical Considerations 
Stability of a Silver Physical Developer 
Silver Image Formation 

A Hypothesis for the Silver Physical Development 
of Latent Prints Residue 

Charge of Latent Print Residue 

Formation of Nucleating Sites on Latent Print Residue 
Formation of Silver Physical Developer Particles 
on Latent Print Residue: Silver Image Formation 
Substrates 

Porous vs. Nonporous Surfaces 
Alkaline Paper 

Preparation and Use of the Silver Physical Developer 
Preparation 

The Acid Pretreatment Reagent 

The Silver Physical Developer Reagent 

The Hypochlorite Post-Treatment Reagent 



Procedure 

Water and Acid Pretreatments 
Silver Physical Development 
Water and Hypochlorite Post-Treatments 
Examples 

The Multi-Metal Deposition Process 
Background 

Porous vs. Nonporous Surfaces 
Formulation and Procedure 

Colloidal Gold Solution (Gold Sol) 

Modified Silver Physical Developer 
Procedure 

More Recent Formulations 
Enhancement Techniques 
Optical Methods 

Photocopying Methods 
Film Photographic Methods 
Digital Imaging Methods 

X-Ray and Scanning Electron Microscopy Methods 
Chemical Methods 
Bleaching 
Intensification 

Radioactive Sulfur Toning and Autoradiography 
Current Research 

Non-Silver Physical Development 
Diffusion Transfer 
Fluorescent Ag-PD 
Test of Effectiveness 
Conclusion 
References 



Introduction 

Background 

Since its introduction to latent print examiners in the mid-1970s, the silver 
physical developer (Ag-PD) has become the standard reagent in many foren- 
sic laboratories to follow ninhydrin for visualizing latent prints on porous 
evidence such as paper. 1 4 The normal process for visualizing latent prints on 



porous surfaces is to first visualize the amine-containing compounds (such 
as amino acids and proteins) using DFO, ninhydrin, 1,2-indanedione, or 
their analogues and then to visualize what remains with the Ag-PD. Most of 
the amine-containing compounds are water soluble and thus their visualizing 
reagents are in a nonaqueous carrier. The Ag-PD is water based and thus it 
visualizes the water-insoluble portion of the latent print residue. These com- 
ponents not only include fats and oils (both of which are lipids) but also 
water-resistant proteins, lipoproteins, and even water-soluble components 
(amino acids, proteins, urea, salts, etc.) that get trapped in the lipids as they 
“dry” and harden (through oxidation). Not all latent print residue contains 
both water-soluble and water-insoluble components together. Some contain 
mostly the former, while some contain mostly the latter. Thus, for porous 
surfaces, both the amine visualizing reagents (DFO, ninhydrin, etc.) and the 
Ag-PD are needed to obtain as many latent prints as possible. At present, no 
reagent has been as successful as the Ag-PD for visualizing the water- insoluble 
components of latent print residue on paper. Thirty-year-old prints on paper 
have been developed on test materials using this reagent. 

Carrier Solvents 

As indicated above, the Ag-PD treatment is normally preceded by an amino 
acid visualization treatment. The carrier solvent for the amino acid visual- 
izing reagents must be nonaqueous because the amine-containing com- 
pounds they visualize are water soluble; an aqueous carrier would wash them 
away. Furthermore, the organic solvent used must not be so strong that it 
dissolves the water-insoluble components that remain. There have been 
numerous formulations over the years for making such reagents. All of these 
contain one major solvent such as acetone, methanol, hexane, heptane, petro- 
leum ether, or Freon 113 (1,1,2-trichlorotrifluoroethane). Of these, acetone 
is the most likely to remove lipids, particularly if they are fresh. For several 
years, Freon was the most favored; however, the current ban on chlorofloro- 
carbons (CFCs) has forced the forensic community to search for other sol- 
vents such as HFC-4310mee (Vertrel XF or 2,3-dihydrodecafluoropentane) 
and FIFE-7100 (methylnonafluorobutane). 5 The carrier solvent for Ag-PDs 
is distilled water rather than tap water, which contains chlorides that cause 
silver to precipitate as silver chloride. Tap water also contains organic species, 
which can reduce silver ions to silver. Water removes ninhydrin-developed 
prints and water-soluble inks (most jet printing inks and certain non-ball- 
point writing inks) from documents. Consequently, the Ag-PD process can 
be detrimental to evidence in other forensic examinations (e.g., handwriting 
and ink analysis). 




The Silver Physical Development Process 

Silver Physical Development in Photographic Chemistry 

The silver physical development process now used to visualize latent prints 
is borrowed from photographic chemistry . 6 ' 10 The emulsion of photographic 
film or paper is a thin coat consisting of photosensitive silver halide crystals 
densely distributed in a gelatin matrix. The photosensitivity of these crystals 
is increased by the presence of a trace amount of silver sulfide specks on their 
surface; these specks are formed when certain sulfur compounds are present 
in the gelatin in trace amounts. A “speck” as used here means a small aggre- 
gate or assembly of atoms or molecules. To develop a silver halide-based 
latent photographic image, early photographic chemists employed the now- 
traditional chemical developer, but they also used the now-photographically 
abandoned silver physical developer. In both cases, the developer distin- 
guishes between photo-exposed and unexposed silver halide embedded in a 
gelatin matrix. Silver physical development is much slower than chemical 
development but it gives a finer grain development. After development, both 
require fixation (e.g., with sodium thiosulfate) to obtain the final developed 
image. 

The Photographic Developers 

As indicated, there are two types of developers for developing latent photo- 
graphic images. A chemical developer contains a reducing agent (a developer 
such as hydroquinone in a basic solution) that selectively reduces only the 
photo-exposed silver halide to metallic silver. A silver physical developer con- 
tains silver ions and a reducing agent that selectively reduces the silver ions 
to metallic silver only on the surface of photo-exposed silver halide. To be 
this selective, the reducing agent is in a state controlled by concentration, 
pH, and sometimes complexing agents. A typical reducing agent used in some 
of the original or classical Ag-PDs consisted of Metol (monoethyl-p-ami- 
nophenol sulfate), which is most active in a slightly basic solution, with some 
citric acid to suppress its activity. Other names for Metol include Elon 
(Kodak), Photol, Pictol, Rhodol, and Veritol . 7,8 The stability of the classical 
Ag-PDs is very low because silver colloids are spontaneously formed in solu- 
tion and these grow uncontrollably until precipitation occurs. Their stability 
was found to increase by adding “protective colloids” such as gum Arabic to 
the formulation . 11 However, it was not until surfactants were better known 
that photographic scientists discovered that cationic surfactants suppressed 
the growth of the spontaneously formed silver colloids, which in most cases 
are negatively charged. This, along with the use of a “controllable” (reversible) 
reducing agent (specifically, the ferrous/ferric redox couple), gave a more 
stable Ag-PD . 12 




Development Centers 

Both the chemical and physical developers selectively act on the photo- 
exposed silver halide crystals rather than on the unexposed. This selectivity 
is caused by the specks of silver (and the sensitizing silver sulfide specks) 
found together only on the surface of the photo-exposed silver halide crystals. 
These specks are referred to as “development sites.” The silver specks are 
formed by the light-induced photochemical reduction of silver halide, and 
the silver sulfide specks result from silver reacting with the traces of “sensi- 
tizing” sulfur introduced into the gelatin. For chemical development, the 
Gurney-Mott theory shows the role of these (Ag and Ag 2 S) specks in the 
chemical reduction of the photo-exposed silver halide crystals on which they 
reside. The reduction of a photo-exposed silver halide crystal to silver metal 
begins on the specks and as reduction occurs, the silver grows from the specks 
as intertwined filaments. For an aggregate of crystals being reduced, the 
filaments intertwine together to form what Walls and Attridge 6 refer to as 
looking like “steel wool.” These aggregates of filaments are black due to light 
getting “trapped” in their configuration (i.e., they bounce the light), and 
because this light is partially absorbed, each reflection attenuates the light. 
For silver physical development, these specks are the nucleation or catalytic 
sites for the reduction of silver ions by the reducing agent, both of which are 
present in the developer. The silver deposits around the specks and forms 
silver particles that begin as colloids ranging in size from 1 nm to 200 nm; 
however, these can grow beyond colloidal size (>200 nm) to form conductive 
layers. The configuration and shape of these particles dictates their color 
appearance. Their color can range from gold, brown, gray, to black. In gen- 
eral, however, these silver colloids are black because in most cases their 
configuration is that of silver strands wrapped into a sphere and such con- 
figurations have light-trapping capabilities. These silver particles grow thicker 
in size rather than in length (like the filaments do), making this process 
suitable for fine grain development. 

Fixation 

As indicated above, placing a photographic film or paper developed by either 
developer in a sodium thiosulfate (hypo) fixing bath gives the final developed 
image. For film or paper chemically developed, the hypo treatment dissolves 
away the unexposed silver halide. The dissolved silver is in the form of a 
silver-thiosulfate complex, Ag(S 2 Q :i ))~. For film or paper physically developed 
(with the Ag-PD), the hypo treatment removes the unexposed silver halide 
and also the photo-exposed silver halide, leaving intact the deposited silver 
that formed around it. If a photographically exposed film or paper is first 
fixed (e.g., with hypo) rather than developed chemically, the fixing process 
removes both unexposed and photo-exposed silver halide, but leaves behind 




(in the emulsion) the silver and silver sulfide nucleating specks that resided 
on the surface of the photo-exposed silver halide crystals. Thus, an Ag-PD 
will develop an image from such post-fixed films/paper. This is referred to 
as post-fixation development. 

Comments 

As can be deduced, silver physical development involves a solution containing 
silver ions and a reducing agent in such combination that the reducing agent 
only reduces the silver ions on the surface of a catalyst (the development 
sites). It is not truly physical, but chemical. However, early photographic 
chemists wished to distinguish such developers from chemical developers by 
noting that the physical developers deposit silver as particles on the latent 
photographic image. For visualizing latent prints, ordinary physical methods 
that visualize by deposition include dry powders, aqueous solutions of col- 
loidal gold, and aqueous solutions of small particles such as molybdenum 
disulfide (MoS 2 ) particles. 

The Silver Physical Development Process of Latent Prints 
on Porous Surfaces 

The discovery that silver physical developers visualize latent prints on porous 
surfaces occurred in the United Kingdom (U.K.). Goode and Morris 13 give 
an excellent history of the development of the Ag-PD in the U.K. The fol- 
lowing is a partial chronology of the development of the current Ag-PD used 
in latent print visualization. 

Jonker, Molenaar, and Dipple 12 (The Netherlands, 1969). These researchers 
from the Philips Research Laboratory in Einhoven, The Netherlands, devel- 
oped an Ag-PD system for photofabricating printed circuit boards. Morris 
(see below) later discovered that this Ag-PD also visualized latent prints on 
paper. In fact, the Ag-PD currently used on latent prints is the Philips for- 
mulation with minor modifications made by Morris. The Philips Ag-PD 
differs from other Ag-PDs used in photographic science in that it is highly 
stabilized. To stabilize it, Jonker et al. used a cationic surfactant and a fer- 
rous/ferric (reversible) redox couple, along with citric acid, to reduce the 
silver ions. The cationic surfactant stabilizes the system by suppressing the 
growth of spontaneously formed (and negatively charged) silver colloids in 
solution. The reversibility of the redox couple, which consists of ferrous and 
ferric ions complexed with citric acid, adds to the stability of the system in 
the following way: it facilitates the control of the system’s potential to deposit 
silver (this potential is given by E cell ) and thus allows one to easily keep this 
potential close to zero (to suppress the formation of spontaneously formed 
silver colloids in solution), but still positive (to allow the reduction of silver ions). 




Collin and Thomas (U.K., 1972). According to Goode and Morris, 13 Col- 
lin and Thomas investigated the use of one of the classical silver physical 
developers to enhance prints developed by the vacuum metal deposition 
process. The idea was sound. These authors knew that silver physical devel- 
opers detect very low levels of silver metal and other metals. It is, for example, 
one of the most sensitive methods that Feigl 11 cites for detecting silver (his 
book was first published in English in 1 93 7) . Thus, they reasoned that because 
the vacuum metal deposition process, after the initial deposition of gold, 
deposits zinc or cadmium all over the surface and in the fingerprint furrows, 
but not on the fingerprint ridges, then an Ag-PD should enhance the furrow 
regions. They noted the potential of its use but were limited by the instability 
of the classical Ag-PD they used. 

Fuller and Thomas 14 (U.K., 1974). These authors also investigated a clas- 
sical Ag-PD for visualizing latent prints on fabrics and paper. They used the 
Metol/ citric acid reducing agent in their Ag-PD. The interesting part of their 
work lies in their Appendix 1 (process modifications). It is surprising that 
many of the ideas they had are now being further investigated. For example, 
regarding their suggestion to use metals other than silver, Dr. Kevin Kyle of 
the Special Technologies Laboratory (a Department of Energy [DOE] Lab- 
oratory located in Santa Barbara, CA) has investigated a copper-based phys- 
ical developer. The DOE funded this project during 1998-1999 and the U.S. 
Secret Service managed the research. Other ideas of Fuller and Thomas 
include sequential treatment with Ag-PD components and film-transfer 
methods. 

Morris 15 (U.K., 1975). Morris was the first to document the use of the 
“Philips Physical Developer” (a name given by Morris to the “FC-1” silver 
physical developer formulated by Jonker, Molenaar, and Dipple in The Neth- 
erlands) for visualizing latent prints on paper. It uses the reversible fer- 
rous/ferric redox couple with citric acid for the reducing agent. The FC in 
the Philips formulation FC-1 stands for ferrous/ferric citric. In our opinion, 
this is Morris’ Ag-PD pioneering work. It introduced the currently used Ag- 
PD. Morris clearly saw the potential of the Ag-PD for visualizing latent prints 
on water-soaked paper (he obtained prints even after 12 days of immersion). 
He saw it as a post-ninhydrin reagent. He also provided a hypothesis for how 
the developer works, proposing that “trigger” materials exist on the latent 
print residue that act as catalytic nuclei and initiate the physical development 
process (similar to the silver and silver sulfide specks on the photo-exposed 
silver halide crystals in photography). These “trigger” materials include: (1) 
wax esters (lipids) because these can strip away the surfactant shell from 
(spontaneously formed) silver nuclei formed in solution, and (2) chloride 




ions (found only on paper that has not been exposed to water) because this 
promotes the formation of silver chloride, which photoreduces to silver 
metal. In both cases, silver nuclei are created on the latent print residue. In 
the first case they are from the silver micelles in solution and in the second 
case they come from the silver ions in solution. Morris only worked with the 
surfactant-stabilized Ag-PD he called the “Philips Physical Developer,” but 
we will see later that removing the surfactant and reducing the silver content 
gives a semi-stable Ag-PD that works as well. Thus, the “surfactant stripping” 
mechanism stated above needs to be modified. We will see later an extension 
of Morris’ hypothesis that states that for Ag-PD to work, the Ag-PD must 
contain negatively charged colloidal silver (or silver sols) in solution. When 
these are sufficiently small, they are attracted to the lipid residue before 
becoming surrounded by the surfactant molecules, if they are in an Ag-PD 
containing a surfactant. 

Knowles etal. 16 (U.K., 1976, 1977, 1978). Knowles and several co-workers 
worked on a series of projects all under the heading “Development of Latent 
Fingerprints on Patterned Papers and on Papers Subjected to Wetting.” In 
addressing prints on patterned paper (paper with high background printing), 
they focused on the radioactive toning enhancement method. Knowles, 
Jones, and Clark (1976) evaluated a radioactive sulfur ( 35 S) toning method; 
Knowles, Lee, and Wilson (1977) performed some operational trials with the 
Sussex Police and, to a lesser extent, with the Metropolitan Police; and 
Knowles, Lee, and Wilson (1978) performed other operational trials. Overall, 
the three series of projects showed that the radioactive toning method was 
feasible and the authors strongly recommended its use. 

Mughal 17 (U.K., 1977). Working as a student at the Police Scientific Devel- 
opment Branch (PSDB), Mughal did an extensive study of cationic surfac- 
tants (all alkylammonium acetates from C 8 to C 18 ). He prepared these and 
tested their micelle forming ability and investigated how micelle age affects 
the rate of silver deposition from an Ag-PD. His research suggested using n- 
dodecylammonium acetate because it was found to give the best stability over 
time (69 hrs). 

Melton and Myers 18 (U.S., 1977). Independent of the work being done in 
the U.K., Melton and Myers of the Battelle Columbus Laboratories (Colum- 
bus, OH) studied several novel latent print visualization methods under 
contract with the Federal Bureau of Investigation (FBI). They also proposed 
silver physical development. Their hypothesis of why it should work had 
some similarities to that of Morris. They said that because the silver nitrate 
method works by the silver ions (1) reacting with halide salts in latent print 




residue and then photochemically reducing to silver and/or (2) getting 
reduced to silver by some reducing agents in the latent print residue, then 
silver physical development should do two things: create the necessary silver 
nuclei for physical development and carry out the physical development. Like 
Fuller and Thomas, they experimented with one of the classical chemical 
developers. Melton and Myers, however, went further and made several Ag- 
PDs using silver nitrate, several chemical developers, and several complexing 
agents. Among the chemical developers used were hydroquinone, ascorbic 
acid, and Elon; among the complexing agents used were di- and tetra-sodium 
EDTA, potassium tartrate and bitartrate, sodium sulfite, citric acid, and 
sodium citrate. The complexing agents where chosen to target either the silver 
ions or the developing agent, or both. {Note: Citric acid also changes the pH 
and, consequently, the reducing ability of the reducing agent used.) They 
made a series of observations and recognized that silver physical development 
had great potential for visualizing latent prints on paper. Although they 
would have recognized this had they been aware of Morris’ pioneering work, 
it is remarkable to note that these two groups were independently studying 
the potential of this reagent. 

Millington 19 (U.K., 1978). Millington studied the effect of light illumina- 
tion on the silver physical development process and found that it influences 
the performance of such developers. It affects the stability of the reagent, the 
rate of development, and generates more background development. 

Hardwick 20 (U.K., 1981). Sheila Hardwick from PSDB was the first (ca. 1984) 
to put the currently used Ag-PD in the police laboratory as a practical reagent 
to use in casework. She distilled the work of others into one operating manual 
or user’s guide. She is also among the first {ca. 1984) to suggest an acidic 
wash pretreatment (using nonchlorinated acids such as maleic acid) to reduce 
background development on basic paper. 

Goode and Morris 13 (U.K., 1983). This report, in our opinion, should have 
been published as a book. It has a wealth of information and, to this day, 
remains one of the most authoritative sources for latent print visualization 
methods. It has laid the foundation for other work. In their section on 
physical development, Goode and Morris discuss the development, proposed 
mechanisms, and use of the surfactant-stabilized silver physical developer. 
Their procedure calls for prewashing with a solution containing an anionic 
surfactant (Terigitol) because they claim that this improves latent print visu- 
alization on surface-coated or plastic materials (such as pressure-sensitive 
plastic tapes), both of which are nonporous. The reasoning, we hypothesize, 
is that the surface area of print residue on nonporous surfaces is not as great 




as that of print residue on porous surfaces and thus an anionic surfactant is 
needed to give the residue a negative ionic character. Basically, the surfactant 
molecule’s neutral, long side chain penetrates the lipid portion of print residue, 
leaving the negative end exposed. The residue thus acquires a negative charge. 
It attracts positively charged micelles to it and provides better “surfactant strip- 
ping.” Apparently, its effectiveness in improving visualization was not that sig- 
nificant because the current procedure does not call for this step; it only calls 
for two prewashes: the distilled water wash and the acidic wash (with a non- 
chlorinated acid) for basic paper. Furthermore, paper washed with a solution 
containing an anionic surfactant would probably not yield any visible prints 
when treated with a surfactant-free Ag-PD (see later discussion). 

Mechanism of Silver Physical Development 

Hereafter, we refer to the currently used silver physical developer as the UK- 
PD. Again, this is the one based on what Morris 15 called the Philips Physical 
Developer. 

Electrochemical Considerations 1 

The key chemical reaction in silver physical developer is the catalytic reduc- 
tion of silver ions by the reducing agent. For this case, where we use the UK- 
PD, the key reactions are 



Ag + + Fe 2+ 


— Ag + Fe 3+ 


(7.1) 


Fe 3+ + H 3 Cit 


— FeCit + 3H + 


(7.2) 


Ag+ + Fe 2+ + H 3 Cit — 


— Ag + FeCit + 3H + 


(7.3) 



where H 3 Cit is the (triprotic) citric acid and Cit 3 ~ is the (trinegative) citrate 
ion. Equation (7.1) is the reduction of the silver ions, Equation (7.2) is the 
formation of the ferric citrate complex. The reaction quotient Q obtained 
from Equation (7.3) is 

Q = [FeCit] [H + ] 3 /[Ag + ] [Fe 2+ ] [H 3 Cit] (7.4) 

This shows the strong dependence of Q on [H + ] and thus on pH. It shows 
that the silver physical development process is highly pH dependent. 

Having chosen the reversible ferrous/ferric redox couple for the reducing 
agent gives the advantage that the process [Equation (7.3)] is reversible and 
therefore treatable as an equilibrium system. Because the process is electro- 
chemical (silver gets reduced to silver metal as ferrous ions get oxidized to 




ferric ions), it can be thought of as an electrochemical cell consisting of two 
vessels connected by a salt bridge. One vessel contains the silver solution and 
the other vessel contains the redox solution. In this case, the driving force of 
the cell is the cell potential, E cell It is also the driving force of the reaction. 
This driving force is obtained from the Nernst equation. At room temperature 
(25°C), this is given by: 

E C eu= E° ell - 59 log Q (millivolts, mV) (7.5) 



where 



E° e ii = E? ed +E° 0X (7.6) 

E° ed is the standard reduction potential for e + Ag + ~ Ag, 

E“ ed =799.6mV (7.7) 

E° x is the standard oxidation potential for Fe 2+ + H 3 Cit -c — FeCit + 3H + + e . 

E° x =-794.6mV (7.8) 



Therefore, 



Eceii = E? ed + E“ x = 5.0 mV (7.9) 

E° x is derived from the oxidation potential of Fe 2+ ^ — — Fe 3+ + er (-771 mV) and 
the formation constant of Fe 3+ + H 3 Cit ^ — FeCit + 3H + (Formation = 0.398). 

The driving force, E cell , of the process and the thermodynamic Gibb’s free 
energy, AG, are related by 



AG = - nFE cell (7.10) 

where n is the number of electrons involved in the electrochemical reaction 
(n = 1 in our case), F is Faraday’s constant (96,487 coulombs/equivalent), 
E cell is in volts (i.e., joules/ coulomb), and AG is in joules. Consequently, a 
positive E cell means a negative free energy and this means the process is 
thermodynamically feasible and can proceed. For the Philips physical devel- 
oper, the cell potential is E cell = 90 mV. Using Equations 7.5 and 7.9, this 
corresponds to Q = 0.03625. The reaction proceeds until equilibrium is 
reached because at equilibrium, AG = 0 and thus E cell = 0 and Q = K eq At 




© 




Figure 7.1 Cationic surfactant molecules surrounding a negatively charged sil- 
ver colloidal particle in a staggered manner, forming a positively charged micelle. 
The silver colloidal particle is negatively charged due to adsorbed citrate ions 

(an 

equilibrium, the potential to deposit silver completely ceases. Because E° elI = 
59 log K eq , then K eq = 1.21. 

Stability of a Silver Physical Developer 

By carefully choosing the concentrations of the components, one can obtain 
a reaction quotient Q such that E cell is small but still positive. This is what 
one wants in designing a stabilized silver physical developer because it sup- 
presses the spontaneous formation of silver particles in solution. 12 The other 
component necessary for stabilizing the developer is the addition of a cationic 
surfactant to keep any spontaneously formed silver particles from growing. The 
spontaneously formed silver particles acquire a negative charge from the sur- 
rounding citrate ions by adsorption (see Figure 7.1). The cationic surfactant 
















surrounds these negatively charged particles, forming micelles. The surfac- 
tant molecules are long-chain alkyl compounds with a positive end (an 
R-NHj group). They arrange themselves on the negatively charged silver 
particle in a staggered way: one with the positive end pointing toward the 
particle and an adjacent one with the positive end pointing outward (see 
Figure 7.1). 12 These micelles have two properties: they are positively charged 
(because the molecules arrange themselves in a staggered way) and they form 
a thick cover. Both of these prevent positive silver ions from approaching 
them and thus prevent their growth. Saunders 21 formulated a simplified 
physical developer (SPD) that contains no surfactant. For it to have any 
stability, he had to significantly reduce the amount of AgN0 3 (by 72%) and 
the ferrous/ferric redox couple (by 25%). It performs well during its stable 
period (about 1 hr) and thus helps to understand the role of the colloidal 
silver with or without using surfactants. 

Silver Image Formation 

The reduction of the silver ions to silver metal by the oxidizing agent occurs 
on nucleation or catalytic sites. In photographic chemistry, where silver phys- 
ical developers were first applied, the catalytic nucleation sites are on the 
photo-exposed silver bromide crystals of the photographic emulsion. The silver 
specks and silver sulfide specks are the actual sites. For visualizing latent prints, 
there is one explanation for the silver physical development of latent prints that 
have not been wetted and several hypotheses for those that have been wetted. 1 

• For the non-wetted (dry) residue, Morris 15 contends that the sodium 
chloride in the latent print residue triggers the physical development. 
The silver ions form an insoluble salt with the chloride ions and the 
resulting silver chloride gets photoreduced to silver with ambient light, 
thus creating the silver nucleation sites. 

• For the wetted residues, a hypothesis being proposed here is that the 
silver physical developer actually provides the nucleation sites as spon- 
taneously formed silver particles attach themselves electrostatically on 
the latent print residue. 

A Hypothesis for the Silver Physical Development 
of Latent Prints Residue 

This chapter section expands on the hypothesis mentioned above that 
requires the Ag-PD to contain spontaneously formed silver particles. Cantu 1 
has discussed several proposed explanations for the silver physical develop- 
ment of latent prints as well as the reasons why such development occurs 
better on porous than on nonporous surfaces. The most likely of the reasons 
for physical development is based on the work by Morris 15 and the ideas of 



Saunders . 22 Both workers recognized the importance of having negatively 
charged silver colloid particles and a low pH in the Ag-PD solution. Both of 
these are present in the UK-PD. The colloidal particles are selectively 
adsorbed on the print residue (which is positively charged), become neutral- 
ized, and function as catalytic nucleation sites for silver physical development. 

Charge of Latent Print Residue 

The reason the print residue is positively charged is that in an acidic envi- 
ronment, residue components containing amine groups (R-NH 2 ) and car- 
bon-carbon double bonds (-C=C-) get protonated . 23 Among the 
compounds with carbon-carbon double bonds in the print residue are the 
unsaturated lipid components and among the amines are insoluble proteins, 
lipoproteins, and even water-soluble proteins and amino acids that get 
trapped in the lipid matrix as the print dries and hardens by oxidation. The 
protonation reactions are 



R-NH 2 + H + 


-> r-nh 3 + 


(7.11) 




H + 




-C=C- + H + 


-> c c 


(7.12) 



Note that another way of providing a positive charge to the residue is by the 
complexation of silver ions with the double bonds in alkenes : 24 



Ag + 

C=C-+Ag + -> CC 



( 7 . 13 ) 



Formation of Nucleating Sites on Latent Print Residue 

As stated, the role of the cationic surfactant in the stabilized UK-PD is to 
suppress the growth of the spontaneously formed and negatively charged 
silver particles. Without the surfactant, these particles grow uncontrollably; 
however, when the surfactant is used, they begin as negatively charged par- 
ticles and gradually grow and reverse their charge until they are fully encased 
with surfactant molecules (micelle formation). At this point they cease to 
grow and are positively charged. These negatively charged particles have an 
electrostatic attraction toward the cationic surfactant molecules; however, in 
the vicinity of the positively charged print residue, they are also attracted to 
the residue. In the proximity of the residue, the attractive forces are compet- 
itive. For particles formed in the bulk solution, micelle formation is dominant 



and this leads to stability; but for particles formed near the residue, particle 
attachment is preferred. The attachment or binding process is not immediate 
and probably requires that the silver particle not grow significantly during 
the process (more on this below). The attachment process neutralizes the 
particles and makes them catalytic nucleation sites for silver physical devel- 
opment. Another way of depositing negatively charged silver particles on the 
positively charged residue is by the “surfactant stripping” process suggested 
by Morris. This involves already-formed silver micelles in the vicinity of the 
print residue and the process is probably slower because both the micelle and 
the residue are positively charged. 

Formation of Silver Physical Developer Particles 
on Latent Print Residue: Silver Image Formation 

Once the print residue acquires the catalytic nucleation sites, silver physical 
development occurs on these sites. The final particles that grow on these sites 
are spherical, about 5 to 40 pm in diameter, and are made up of strands of 
silver (see Figure 7.2). The gray to black color of these particles is attributed 
to their size and configuration. The print image is made up of a dense 
accumulation of these particles. 



Substrates 

Porous vs. Nonporous Surfaces 

Silver physical developers visualize latent prints better if they are on porous 
or semiporous surfaces rather than on nonporous surfaces. On porous sur- 
faces, latent print residue enters into and spreads throughout the porous 
structure. It thus has a greater surface area and is more exposed than on a 
nonporous surface. Because of this, more nucleating sites are formed on such 
residue and silver physical development (silver particle deposition and 
growth) occurs sooner and to a greater extent. Another reason why Ag-PDs, 
whether (cationic) surfactant stabilized or not, do not visualize latent prints 
on nonporous surfaces well is because newly formed, negatively charged silver 
particles grow. With a cationic surfactant, they also grow but after a certain 
point their growth is reduced and their charge is reversed. That is, these 
developers cannot retain particles of a fixed size and concentration long 
enough for a sufficient number of them to adhere to the latent print residue. 
Although the use of colloidal gold to create nucleation sites for subsequent 
silver physical development is discussed later, it is sufficient to say that treat- 
ment with negatively charged, fixed-size colloidal gold particles (at suffi- 
ciently low pH to create a positive residue) does bring about sufficient particle 




Figure 7.2 Scanning electron microscope (SEM) images of silver particles 
adhered to paper fibers with print residue. (Images taken by Jim Young and Gary 
Mong, Pacific Northwest National Laboratory, Richland, WA.) 






Figure 7.2 (continued) 



adherence on residue that is on porous or nonporous surfaces. However, on 
nonporous surfaces, the colloidal gold treatment can take up to 120 min to 
have a sufficient amount of particles adhere to latent print residue. 



Alkaline Paper 

Alkaline paper has a pH > 7, as opposed to acid paper which has a pH < 7. 
Paper with calcium carbonate filler is alkaline. The alkalinity results from 
calcium carbonate being a salt of a weak acid (carbonic acid) and a strong 
base (calcium hydroxide). Although it is practically insoluble in water, it 
dissolves, then hydrolyzes and produces a basic solution. If alkaline paper is 
treated with an Ag-PD, it turns black, which upon drying sometimes turns 
brownish-black; the most likely reason for this is that the silver physical 
developer becomes destabilized by the paper — and only in the vicinity of 
the paper — causing the developer to deposit silver, silver oxide, and/or ferric 
oxide on the paper. To elaborate on this, the alkalinity of the paper causes a 
local change in pH, which causes destabilization. The destabilization causes 
a premature reduction of silver on the paper. The hydroxide ions locally 
formed in the paper react with the developer’s ferric ions and silver ions to 
produce insoluble ferric hydroxide and silver hydroxide, respectively, on the 




paper and these convert to ferric oxide (Fe 2 0 3 or rust) and silver oxide (brown- 
black Ag 2 0), respectively, upon drying. To avoid this, alkaline paper is neu- 
tralized by treating it with acid. The acid, however, must not be a chlorinated 
acid (such as hydrochloric acid) because this introduces chloride ions, which 
react with silver to produce photosensitive silver chloride. Hardwick 20 intro- 
duced the use of maleic acid. The concentration currently used is 2.5% (w/v). 
The Forensic Science Services (FSS) in London, U.K. uses a dilute solution 
(1%) of nitric acid. 25,26 Others have used a 2.5% (w/v) malic acid solution, 
which is less costly than maleic acid. Household vinegar (5% acetic acid) 
works as well. 27 The paper is treated until all bubbling ceases. The net reaction 
that takes place is: 

CaC0 3 + 2H + — > Ca 2+ + H,0 + CO, (gas) (7.14) 



Preparation and Use of the Silver Physical Developer 
Preparation 

During preparation of the reagents associated with the silver physical devel- 
opment process, protective attire such as gloves, labcoat, protective eyewear, 
and mask should be worn. All containers used during the process should be 
rinsed with distilled water prior to use. 

The Acid Pretreatment Reagent 

Acids containing chlorine (e.g., hydrochloric acid) should not be used. A maleic 
acid solution is recommended, although as indicated above, dilute nitric or 
acetic acid also work. The maleic acid solution is made by thoroughly mixing 
25 g maleic acid into 1 1 distilled water. This solution has an indefinite lifetime. 

The Silver Physical Developer Reagent 

The following formulation is for the UK-PD. 1_4,13 ’ 15 It involves preparing three 
stock solutions and a working solution from these. The three stock solutions 
are made as follows and in the order given: 

1. Ferrous/ferric redox solution (with citric acid) stock solution: 

a. Measure 900 ml distilled water into a clean container. 

b. Thoroughly dissolve 30 g ferric nitrate (nonadyrate) into the dis- 
tilled water. 

c. Thoroughly dissolve 80 g ferrous ammonium sulfate (hexahydrate) 
into the above solution. 




d. Thoroughly dissolve 20 g citric acid (anhydrous) into the above 
solution. 

e. The final solution should contain no undissolved crystals. 

2. Detergent solution 

a. Measure 1 1 distilled water into a clean container. 

b. Thoroughly dissolve 4 g n-dodecylamine acetate into the distilled 
water. 

c. Thoroughly dissolve 4 g Synperonic-N into the above solution. 

3. Silver nitrate solution 

a. Measure 100 ml distilled water into a clean container. 

b. Thoroughly dissolve 20 g silver nitrate into the distilled water. 

c. Once the silver nitrate has totally dissolved, store the solution in an 
amber glass bottle. 

These stock solutions have an indefinite lifetime. The detergent solution may 
have a slightly cloudy appearance while the other two solutions should be 
clear. The working solution is made as follows and in the order given: 

• Measure 900 ml redox solution into a clean container. 

• Add 40 ml detergent solution to the above solution and thoroughly 
mix for approximately 5 min. 

• Add 50 ml silver nitrate solution to the above solution and thoroughly 
mix for about 5 min. 

The lifetime of the working solution is between 1 and 2 weeks. If a white 
precipitate begins to form at the bottom of the container, a new solution 
should be made. 

The Hypochlorite Post-Treatment Reagent 

This reagent consists of a 1:1 (v/v) dilution of a household “chlorine” bleach 
with water (50% dilution). These bleaches contain between 5 and 6% sodium 
hypochlorite. Some use a 3:1 (v/v) water:bleach solution (25% dilution). This 
solution is stable indefinitely. 

Procedure 

In the procedure used by the U.S. Secret Service, one clean glass tray is used 
for all the treatments: water pre-wash, acid pre-wash, Ag-PD treatment, and 
hypochlorite post-wash. The solutions are disposed of properly (check local 
regulators) after each step. In some cases, the Ag-PD and maleic acid can be 
reused; however, this depends on the number of items processed and the 
nature of the contaminants on the items (e.g., reagents are not reused if they 
processed items with biohazardous contaminants). 




Water and Acid Pretreatments 

The water pretreatment involves distilled water and is used to remove any 
dirt or debris that may be present on the evidence. It will also remove 
ninhydrin-developed prints and stains as well as water-soluble inks. The acid 
pretreatment is absolutely necessary for basic papers because these usually 
contain (alkaline) calcium carbonate. 

Silver Physical Development 

This part of the process produces the visible prints, with their color ranging 
from gray to black. It should be performed in subdued light because silver 
nitrate can photo-reduce to silver and increase background development; it 
also reduces the activity of the developer. Prints begin to appear within 5 to 
10 min and processing should stop once sufficient contrast is achieved. Pro- 
cessing time ranges from 10 to 30 min. 

Water and Hypochlorite Post-Treatments 

Once the development is complete, the evidence is washed in running tap 
water. Some recommend distilled water because tap water produces colloidal 
size silver chloride particles that can become lodged in the paper and darken 
with time. We have found that using running water for about 5 min gets rid 
of these particles and chemicals from the Ag-PD (e.g., ferric, ferrous, and 
silver ions). To enhance the darkness of the print and lighten the background 
(assuming the background is not high in silver physical development), Phil- 
lips et al. 2 found that treating the evidence with a 50% solution of household 
bleach (hypochlorite) for approximately 2 to 3 min gave this result. If the 
background is high in silver physical development, then it too will darken. 
The reaction occurring is the conversion of silver to silver oxide. After this, 
the evidence is washed again in running tap water and dried; drying can be 
done with a photodryer. The evidence is photographed using film. The result- 
ing photograph can be digitally scanned for digital enhancement. 

Examples 

This chapter section provides casework examples of additional prints developed 
by the Ag-PD process, ninhydrin prints enhanced by the Ag-PD, Ag-PD prints 
enhanced by hypochlorite, and Ag-PD prints enhanced by digital processing. 

Figure 7.3 compares a ninhydrin palm print on a letter and the same letter 
after Ag-PD treatment. The Ag-PD process brought out an additional finger- 
print in the middle of the palm print. Figure 7.4 shows how the Ag-PD process 
enhanced a ninhydrin print on a forged United States Treasury check. Figure 7.5 
shows two things: the enhancement of a ninhydrin print on a counterfeit $20 
note and the removal by the Ag-PD treatment of the jet ink that printed the 
counterfeit. Figure 7.6 shows an Ag-PD print before and after enhancement with 




Figure 7.3 Comparison of a ninhydrin palm print on a letter before (top) and 
after Ag-PD treatment (bottom). Additional fingerprint is revealed. 

hypochlorite bleach; and Figure 7.7 compares an Ag-PD print on a forged check 
with a patterned background and the same print after removing the background 
digitally using the Fast Fourier Transform (FFT) technique. 





Figure 7.5 Comparison of a ninhydrin print on a counterfeit $20 note before 
(left) and after Ag-PD treatment (right). Ninhydrin print is enhanced and ink 
(from inkjet printer) is removed. 



The Multi-Metal Deposition Process 
Background 

Saunders 28,29 introduced the multi-metal deposition (MMD) method for 
visualizing latent prints on porous and nonporous surfaces. It is a modifica- 
tion of a biochemical technique used for staining proteins . 30 The method 





Figure 7.6 Comparison of an Ag-PD print on a counterfeit $20 note before (left) 
and after hypochlorite bleach treatment (right). Ag-PD print darkens and back- 
ground lightens. 



involves treating the test species (proteins in the biochemical case and latent 
prints in our case) with a colloidal gold solution (having a pH ~ 2.7) and 
then with a weak solution of silver physical developer. The colloidal gold 
particles are highly negatively charged and thus bind strongly with the target 
species to form catalytic nucleating sites for silver physical development. In 
this technique, one speaks of silver amplifying the gold image. 

Porous vs. Nonporous Surfaces 

As indicated above, compared to the silver physical development method, 
which visualizes latent prints on porous rather than nonporous surfaces, the 
MMD method is able to visualize prints on both surfaces. Silver physical 
developers form and supply the colloidal particles that bind to the latent 
print residue and these become the critical catalytic nucleating sites. Once 
these particles bind, they then grow in the development process. The MMD 
method, on the other hand, supplies already-formed colloidal particles that 
do not grow and can thus build up if given sufficient time. They grow only 
during the silver physical development stage as silver builds up on them. 
Recall that for binding to occur, the silver or gold particles must reside on 
the latent print residue for a sufficient amount of time without growing 
significantly. Thus, for nonporous surfaces (where the surface area of the 
latent print residue is less expansive than on a porous surface), the MMD 
method must be given enough time to form a sufficient number of gold 





Figure 7.7 Comparison of a ninhydrin print on a forged check with patterned 
background before (top left) and after Ag-PD treatment (top right) and after 
subtracting the patterned background using digital FFT methods (bottom). 

nucleating sites so that good contrast is obtained with silver amplification. 
For porous surfaces, some investigators have found the MMD method results 
in excessive background development. This will occur if the unbound gold 
(i.e., gold particles that get occluded in the paper fibers) is not properly 
removed. This is why the washing procedure after the gold treatment is very 
important. 



Formulation and Procedure 29 
Colloidal Gold Solution (Gold Sol) 

To prepare this solution, one needs a 10% (w/v) tetrachloroauric acid stock 
solution, a 1% (w/v) trisodium citrate stock solution, a 0.5 M (9.6% w/v) 
citric acid stock solution, and Tween 20 (a non-ionic surfactant/ detergent). 
The stock solutions must be made with distilled or deionized water (i.e., it 
must be free of divalent ions, chlorine, and organic substances). These stock 
solutions are stable indefinitely. To prepare 1 1 of the colloidal gold working 
solution, add 1 ml of the 10% tetrachloroauric acid stock solution to 1 1 
distilled water and bring to a boil. Rapidly add 10 ml of the 1% trisodium 
citrate stock solution and continue boiling gently for 10 min. The resulting 
colloidal gold solution should be “port wine” in color. Turn off the heat and 
add 5 ml Tween 20. Mix well and let cool to room temperature. When cool, 
add 10 ml of a 1% polyethylene glycol (molecular weight 10-15,000) and 
adjust the pH to 2.7 with 0.5 M citric acid (about 1 ml). Restore the volume 
to 1 1 with distilled water. Store in clean glass or plastic container in a refrig- 
erator. The gold sol is stable for at least 3 months. The gold colloidal particles 
prepared in this way have an average size of about 30 nm. Margot and 
Lennard 3 use 15 ml trisodium citrate instead of 10 ml and exclude the poly- 
ethylene glycol. 

Modified Silver Physical Developer 

Two stock solutions are needed: a ferrous/ferric redox couple stock solution 
and a 20% (w/v) silver nitrate solution. These stock solutions have an indef- 
inite shelf life when stored in clean glass bottles (dark glass for the silver 
nitrate solution). The redox stock solution is prepared by sequentially dis- 
solving into 1 1 distilled water, 33 g ferric nitrate nonahyrate, 89 g ferrous 
ammonium sulfate hexahydrate, 22 g citric acid, and 1 ml Tween 20. The 
working solution (the modified silver physical developer) is prepared by 
adding one part 20% silver nitrate solution to 99 parts of redox solution. The 
working solution should be prepared just prior to using because it is only 
stable for about 15 min. Saunders later revised the formulation of the redox 
stock solution to be about half as concentrated (16 g ferric salt, 43 g ferrous 
salt, 11 g citric acid, and 0.25 ml Tween 20). This provides the same results 
but less quickly. 

There are two points to be noted. First, a non-ionic surfactant is used 
instead of a more stabilizing cationic surfactant. Cationic surfactants prevent 
the silver from depositing around the bound gold particles. One reason for 
this may be that the bound gold particles are not fully neutralized and the 
cationic surfactant surrounds them, forming a protective shield that keeps out 
silver ions. Second, the amount of silver in the final developer is sufficiently low 




(0.2%) to not form silver oxide when used in alkaline paper; therefore, there 
is no need to neutralize alkaline paper. This, in fact, is fortuitous because 
neutralization produces unwanted calcium ions (see below). 

Procedure 

Porous items should be prewashed several times with distilled water for 20 
to 30 min. A maleic acid pretreatment should be avoided for alkaline paper 
as this creates divalent calcium ions which destabilize the colloidal gold 
solution. Nonporous items only need a single distilled water prewash of about 
10 min unless they are quite dirty (then several washes are necessary). Soak 
the items in the colloidal gold solution for 30 to 120 min, but avoid over- 
development. Rinse the items in distilled water. For paper, rinse in several 
changes of distilled water for 15 min or more. Any gold colloids that are 
trapped/occluded in the paper fibers must be removed to reduce background 
interference. Place the items in freshly prepared modified silver physical 
developer for 5 to 15 min. Silver amplification takes place almost immedi- 
ately; therefore, the items should be removed once good contrast between 
the print and background is obtained. Finally, rinse in tap water to remove 
excess developer, air dry, and photograph. 

More Recent Formulations 

Since Saunders’ work, most of the research performed on the MMD method 
has been by Dr. Bertrand Schnetz, who obtained his Ph.D. doing this work 
at the Institut de Police Scientifique et de Criminologie, University of Lau- 
sanne (Switzerland). In 1993, 31 Schnetz experimented with replacing colloidal 
gold with protein-bound colloidal gold. This would bind to the latent print 
residue and then this would be amplified with enzymes or stains forming 
colored or fluorescent products. In 1997, he introduced the MMD II method. 
It recommends using siliconized glassware and colloidal gold particles with 
a particle size diameter of 14 nm (compared to 30 nm for the Saunders 
MMD). Recently, Schnetz published his most recent optimization of the 
method. 32 



Enhancement Techniques 

For silver physically developed prints that are weak or have a strong interfering 
background, one can use several enhancement techniques to improve the 
contrast between the print and its background. The latter includes prints on 
dark or highly patterned surfaces. The enhancement techniques can be 
grouped into at least three classes: optical, physical, and chemical. Because a 
detailed description of these is already available, 1 they are only summarized 





here. The optical or photoreproductive methods include simple photocopy- 
ing methods, standard film photographic methods, and digital image capture 
methods. 

Optical Methods 
Photocopying Methods 

Photocopying methods are usually used to intensify a weak print. The effect 
is caused in part by the high contrast their images are meant to have, but 
also by the fact that the spectral sensitivity of their “cameras” is different 
from that of the human eye. In the latter case, if the spectral sensitivity reaches 
out into the near-infrared region, the contrast of certain background colors 
weakens while that of the Ag-PD print does not. (“Ag-PD” is also used as an 
adjective to mean silver physically developed.) 

Film Photographic Methods 

The versatility available to both film and digital photographic methods 
includes the choice of illuminating and viewing filters. In fact, use of laser 
illumination or illumination from an alternate light source is often used in 
photographing evidence. With film photography, one also has a choice of 
films of different sensitivities and of chemical development methods. Thus, 
photographic enhancement techniques involve a judicious choice of illumi- 
nating filters, viewing filters, film sensitivities, and processing methods to 
obtain the optimum contrast from a latent print image. 

Digital Imaging Methods 

As with film photography, digital photography also uses diverse illuminating 
and viewing filters. Similar to the human eye, photographic films, CCD 
cameras, optical scanners, and digital cameras have their own spectral sen- 
sitivities and this plays a critical role in the enhancement scheme. However, 
the greatest advantage of capturing a digital image is what can be done with 
the image afterward. Image processing software that is designed to enhance 
image contrast includes Image-Pro (from Media Cybernetics) and Photoshop 
(from Adobe). Combining this enhancement capability with the choices of 
filtered illuminating/viewing conditions provides a powerful approach to 
optimize contrast. For example, the image of an Ag-PD print on a colored 
background viewed at two separate wavelengths can be manipulated to 
remove the background. This follows because the silver image has the same 
level of gray over a large spectral range but not the colored background. Also, 
well-defined patterned backgrounds can be removed by Fourier transform 
methods. Images can be taken before and after development and compared 
to remove background completely. 




X-Ray and Scanning Electron Microscopy Methods 

Because silver is X-ray opaque, an Ag-PD print, which consists of a dense 
collection of silver particles (see Figure 7.2), should attenuate X-rays. Images 
of such prints can be obtained using transmission soft X-ray methods but 
the print resolution is not as high as that of prints on images obtained using 
other X-ray methods. One is scanning electron microscopy (SEM) equipped 
with an X-ray fluorescence detector capable of doing elemental mapping, 
and the other is SEM capable of generating a backscatter electron image. The 
latter has been used in the U.K. to eliminate background printing from Ag- 
PD prints on dark printed surfaces. For this to work, the background (which 
is normally printing) must not contain materials that cause silver physical 
development! Certain inks contain lipids, colloidal metallic salts, and metal- 
lic-based dryers that can potentially promote silver physical development. 

Chemical Methods 

Because an extensive review of the chemical methods that have been devel- 
oped and used mostly in the U.K. to enhance Ag-PD prints is already avail- 
able, 1 only a few are briefly discussed here. In any of these methods, a prewash 
step must be performed to remove as much as possible the following sub- 
stances that may be on or in the paper: ferrous, ferric, silver and calcium 
ions, ferric citrate, silver chloride particles (formed by washing with tap water), 
and silver particles (either from the solution or formed on/in the paper back- 
ground). Some of these may be difficult to remove, particularly the particles 
that are well attached to or occluded in the paper and ions that strongly adhere 
to cellulose fibers. Saunders 33,34 recommends washing with distilled water that 
contains 1% (v/v) Tween 20, with at least three changes of water. 

Bleaching 

These methods replace silver, which is gray to black in color due to its 
configuration (see Figure 7.2), with a substance of lighter color. They are 
used to lighten Ag-PD prints that appear on dark surfaces. The methods 
developed by Morris and Wells 35 are mostly borrowed from photographic 
chemistry and those of Saunders 33,34 are based on silver chemistry. In both 
cases, the conversion of silver is to a silver halide: silver bromide, silver 
chloride, or silver iodide. The conversion is usually performed under subdued 
light because these substances are photosensitive and can revert back to silver 
(though in a different configuration). Morris and Wells 35 cite two methods 
for forming the bromide: via oxidation with Br,/KBr and via oxidation with 
K 3 Fe(CN) 6 /KBr. Saunders prepares the silver chloride using a dilution of the 
ferrous/ferric (citric acid) redox system and table salt. He forms the silver 
iodide using ferrous/ferric (citric acid) redox system and KI. 



Intensification 

These methods are used to enhance weak Ag-PD prints. There are at least 
four methods. The simplest of these is redipping in Ag-PD. This causes 
further development on existing silver particles contributing to their growth. 
It does not always add new particles to give a greater density of particles and 
also it could increase the build-up of silver in the background. Goode and 
Morris 13 proposed an intensification method that involves conversion of the 
silver to silver sulfide (Ag,S), followed by silver physical development using 
a nitrate/nitrite redox couple. Saunders suggests a rather novel intensification 
method that uses the ferrous/ferric (citric acid) redox couple and a dilute 
sodium chloride (NaCl) solution. Its mechanism is not fully understood. The 
fourth method involves sodium hypochlorite (NaOCl). A 25 to 50% solution 
of household bleach, which is 5 to 6% NaOCl, lightens the background and 
intensifies the print. The most likely mechanism is that silver oxide (Ag 2 0) 
is formed. Except for the redipping method, all of these methods change the 
composition and surface characteristics of the original silver particle and 
both changes contribute to its change and intensification in color. 

Radioactive Sulfur Toning and Autoradiography 

This method was developed in the U.K. 36 for removing interfering back- 
ground from Ag-PD prints. It involves converting the silver to radioactive 
silver sulfide (Ag 2 35 S), where 35 S is the (3-emitting radioactive isotope of sulfur 
used, followed by autoradiography for imaging. As mentioned for the X-ray 
methods, if the background contains printing, the ink must not contain mate- 
rials that cause silver physical development to occur. If it does, any silver particles 
on the printing will also be converted to silver sulfide and be radio-imaged. 



Current Research 



Non-Silver Physical Development 

There are at least two problems of economics with Ag-PDs: the silver is 
expensive and about 20 to 50% of it is not used during the useful lifetime of 
the developer. 26 The latter fact indicates that the developer is rather inefficient 
and that a good portion of silver is thrown away when the exhausted Ag-PD 
solution is disposed. At present, there is no way to replenish used Ag-PD. In 
1969, Jonker et al. 12 mentioned ways of making non-noble metal physical 
developers and later, in 1976, 37 Molenaar et al. worked on optimizing the 
copper physical developer. Dr. Kevin Kyle from the Special Technologies 
Laboratory, Santa Barbara, CA, assisted the United States Secret Service 
(USSS) in adapting the copper physical developer of Molenaar et al. 37 for 
visualizing latent prints on paper. Preliminary results show promise, but there 




is much to be done to optimize the system. This work was supported by the 
Special Technologies Program of the U.S. Department of Energy. 

Diffusion Transfer 

The USSS is investigating a method of transferring Ag-PD prints onto pho- 
tographic paper or film. The method is based on ideas of Dr. Edwin Land 
during his development of the Polaroid transfer method. 38 The actual process 
is referred to as diffusion transfer. 39 To perform the transfer, one needs two 
items: receiver paper/film and an activator solution. The receiver paper/film 
is a gelatin-coated material in which the gelatin contains activation sites for 
silver physical development and the activator is a photographic developer 
(e.g., hydroquinone) plus hypo (sodium thiosulfate). The transfer materials 
currently being tested by the USSS are Kodak PMT matt receiver paper and 
Kodak PMT activator. For transferring an Ag-PD print onto the paper/film, 
the silver image is first converted to a silver bromide image using any of the 
bromination methods. The brominated print is then placed on the receiver 
paper/film and after this some activator solution is placed on the back of the 
paper with the print. This is pressed with a rubber roller and then the paper 
with the print is carefully lifted from the receiver paper/film. The receiver 
paper/film, which now contains the print image without background, is 
allowed to dry. As mentioned, if the background is printing with ink that 
causes silver physical development, then this will also transfer. At present, 
this project is still under development. 

Fluorescent Ag-PD 

The idea of converting the silver image of an Ag-PD into a fluorescent image 
has enormous advantages; it strengthens the contrast of weak prints and it 
removes background interference (i.e, if the background is not printed with 
ink that promotes silver physical development). Thus far, there has been no 
simple conversion of silver to a silver fluorescent compound. What has been 
done is borrowed from photographic “toning” chemistry. In the mid-to-late 
1920s, motion picture photographic scientists created ways to change a silver 
image into colored images. 40 One that formed a red image involved a 
rhodamine dye. At the time, the interest was in the red color product and 
not its fluorescent properties. Under USSS guidance and with support from 
the Special Technologies Program of the U.S. Department of Energy, Dr. 
Kevin Kyle of the Special Technologies Laboratory, Santa Barbara, CA, mod- 
ified the photographic chemistry to apply it to an Ag-PD print. The resulting 
print fluoresces in the furrow areas rather than on the ridges and there is no 
background fluorescence. The mechanism is rather detailed 1 and is not dis- 
cussed here. 




Test of Effectiveness 



Currently in our laboratory the effectiveness of an Ag-PD is crudely tested 
using a test paper strip with a spot of gold chloride on it. The density of the 
gold chloride spot (gold chloride/ area) is high because it is made with a 
relatively concentrated (20 mg/1) gold chloride solution. The Ag-PD reduces 
the gold chloride to elemental gold and this catalyzes the deposition of silver. 
It only tests if the Ag-PD deposits silver on nucleation sites — not how well 
or how fast. Barford et al. 26 observed that the ferrous ion and silver ion 
concentrations were the most critical factors affecting the effectiveness of an 
Ag-PD. They found that the UK-PD performed best (with development time 
<20 min) when the silver ion concentration does not fall below 50% of its 
original concentration and the ferrous ion concentration does not fall below 
60% of its original concentration. Seeing the importance of obtaining these 
concentrations, they determined the ferrous ion concentration using poten- 
tiometric titration and the silver ion concentration using a silver/sulfide solid- 
state electrode. Currently, Dr. Kyle is working on an alternate way of obtaining 
the ferrous ion concentration. 41 Also, Cantu is currently working with the 
Institut de Police Scientifique et de Criminologie (University of Lausanne, Lau- 
sanne, Switzerland) in developing a test strip containing gold chloride spots of 
equal size but of decreasing density. The test strip is placed into the Ag-PD at 
two different times to estimate the rate and sensitivity of development. 



Conclusion 



Silver physical developer is a powerful reagent for recovering latent prints on 
porous surfaces that the amino acid visualizing reagents failed to develop. It 
works on the water-insoluble components of latent print residue and, conse- 
quently, works on water-soaked evidence. When it is used after a colloidal gold 
pretreatment, its working ability is extended to nonporous surfaces. A mecha- 
nism by which it works has been proposed. It is built on several observations 
and offers avenues one can take to improve the current or create new physical 
developers. At present, the U.S. Secret Service uses about 1 600 liters (423 gallons) 
of Ag-PD annually. It has increased the number of prints found on evidence 
and brought about more convictions than when ninhydrin was used alone. 



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41. Kyle, K., personal communication, 1999. 




Automated Fingerprint 
Identification and 
Imaging Systems 

ANIL JAIN 

SHARATH PANKANTI 




Contents 

Introduction 
Emerging Applications 
System Architecture 
Challenges 

Inconsistent Contact 
Non-uniform Contact 
Irreproducible Contact 
Feature Extraction Artifacts 
Sensing 

Fingerprint Sensing 
Fingerprint Representation 
Minutiae Feature Extraction 
Orientation Estimation 
Segmentation 
Ridge Detection 
Minutiae Detection 
Post-processing 
Fingerprint Classification 
Fingerprint Matching 
Fingerprint Enhancement 
Large-Scale Systems Issues 
System Evaluation 
Conclusions and Future Prospects 
Acknowledgments 
References 



Introduction 



More than a century has passed since Alphonse Bertillon first conceived and 
then industriously practiced the idea of using body measurements for solving 
crimes. 1 Just as his idea was gaining popularity, it faded into relative obscurity 
because of the far more significant and practical discovery of the uniqueness 
of the human fingerprint.* Soon after this discovery, many major law enforce- 
ment departments embraced the idea of first “booking” the fingerprints of 
criminals so that their records are readily available and later using leftover 
fingerprint smudges (latents), so that the identity of criminals can be deter- 
mined. These agencies sponsored a rigorous study of fingerprints, developed 
scientific methods for visual matching of fingerprints and strong pro- 
grams/cultures for training fingerprint experts, and applied the art of finger- 
print identification for nailing down the perpetrators. 

Despite the ingenious methods improvised to increase the efficiency of 
the manual method of fingerprint indexing and search, the ever-growing 
demands on manual fingerprint identification quickly became overwhelm- 
ing. The manual method of fingerprint indexing resulted in a highly skewed 
distribution of fingerprints into bins (types): most fingerprints fell into a few 
bins and this resulted in search inefficiencies. Fingerprint training procedures 
were time-intensive and slow. Further, demands imposed by painstaking 
attention needed to visually match the fingerprints of varied qualities, the 
tedium of monotonic nature of the work, and increasing workloads due to 
a higher demand on fingerprint identification services all prompted the law 
enforcement agencies to initiate research into acquiring fingerprints through 
electronic media and automatic fingerprint identification based on the digital 
representation of the fingerprints. These efforts have led to the development 
of automatic/semi-automatic fingerprint identification systems over the past 
few decades. This chapter attempts to present the current state-of-the-art in 
fingerprint sensing and identification technology. 

The objective is to present a high-level overview of fingerprint sensing 
and matching technology so as to provide the reader with some insights into 
the strengths and limitations of the automation in matching fingerprints. 
Because of space limitation, the focus is only on the core technology rather 
than the details of the commercial systems. The existing elaborate manual 
protocols (e.g., What is a core? How are fingerprints indexed/filed in a manual 
system?) are not described for similar reasons. Readers are referred to Ref- 
erence 2 for an excellent exposition on these subject matters. 

The remainder of this chapter is organized as follows: introduction of 
emerging applications of automatic fingerprint matching and its implications; 



* In 1983, the Home Ministry Office, U.K., accepted that no two individuals have the same 
fingerprints. 




Table 8.1 Biometric Applications 



Forensic 


Civilian 


Commercial 


Corpse identification 


National ID 


ATM 


Criminal investigation 


Driver’s license 


Access control 


Parenthood determination 


Welfare disbursement 


Cellular phone 




Border crossing 


Credit card 



From Jain, A.K., Hong, L., and Pankanti, S., Biometric identification, Commun. 
ACM , 91-98, Feb. 2000. 



description of functional components of a typical fingerprint identification 
system; summary of some of the challenges involved in automatic fingerprint- 
based identification; discussion of topics related to fingerprint sensing technol- 
ogy; description of the issues related to representing the useful information 
contained in a fingerprint image; presentation of automatic extraction of the 
most commonly used fingerprint representation (i.e., minutiae); an overview 
of fingerprint classification and matching algorithms; a summary of a finger- 
print image enhancement algorithm; issues peculiar to large-scale identification 
systems; and fingerprint identification system performance evaluation issues. 



Emerging Applications 

As mentioned, law enforcement agencies were the earliest adopters of fingerprint 
identification technology. More recently, increasing identity fraud has created a 
growing need for biometric technology* for positive person identification in a 
number of non-forensic applications. Is this person authorized to enter this 
facility? Is this individual entitled to access the privileged information? Is the 
given service being administered exclusively to the enrolled users? Answers to 
questions such as these are valuable to business and government organizations. 
Because biometric identifiers cannot be easily misplaced, forged, or shared, they 
are considered more reliable for personal identification than traditional token- 
or knowledge-based methods. Table 8.1 summarizes typical applications of bio- 
metrics for positive person identification. The objectives of these applications 
are user convenience (e.g., money withdrawal without ATM card and PIN), 
better security (e.g., difficult to forge access), and more efficiency (e.g., lower 
overhead for computer password maintenance). 

A significant limitation of the existing biometrics-based personal iden- 
tification systems is that their accuracy performance is not perfect. These 
systems sometimes falsely accept an impostor (false accept error) and falsely 
reject a genuine user (false reject error). Typically, the two error rates depend 



* Biometrics refers to use of distinctive physiological (e.g., fingerprints, face, retina, iris) and 
behavioral (e.g., gait, signature) characteristics for automatically identifying individuals. 3 




False Accept Rate (FAR) 

Figure 8.1 Receiver operating characteristics (ROC) curve of a system illustrates 
false reject rate (FRR) and false accept rate (FAR) of a matcher at all operating 
points (threshold, T). Each point on an ROC defines FRR and FAR for a given 
matcher operating at a particular threshold. High security access applications are 
concerned about break-ins, and hence operate the matcher at a point on ROC 
with a small FAR. Forensic applications desire to catch a criminal even at the 
expense of examining a large number of false accepts, and hence operate their 
matcher at a high FAR. Civilian applications attempt to operate their matchers 
at the operating points, with both low FRR and low FAR. (From Jain, A., Bolle, 
R., and Pankanti, S., Biometrics: Personal Identification in Networked Society, 
Kluwer, Massachusetts, December, 1999.) 

on the system operating point (called decision threshold) and their relation- 
ship is characterized by a receiver operating characteristic (ROC). Figure 8.1 
illustrates a hypothetical ROC and typical operating points for different 
biometric applications. 

Tremendous success of fingerprint-based identification technology in law 
enforcement applications, decreasing cost of the fingerprint sensing devices, 
increasing availability of inexpensive computing power, and growing identity 
fraud/theft have all ushered in an era of fingerprint -based person identifica- 
tion applications in commercial, civilian, and financial domains. 

A typical law enforcement identification system serves a different purpose 
than those of the emerging biometric applications. Most of the financial and 
commercial applications require identity verification (also known as authen- 
tication), which involves confirming/denying a claimed identity based on 
fingerprint information, given a claim to a specific identity (e.g., Joe Smith). 



That is, given a fingerprint known to have originated from, for example, Joe 
Smith’s left index finger and another print from a left index finger, the system 
will determine whether the second print, indeed, belongs to Joe Smith. The 
law enforcement systems, on the other hand, primarily deal with recognition 
(also popularly referred to as identification, as in automatic fingerprint iden- 
tification system), which involves establishing the identity of the person based 
on the fingerprint information. Given a fingerprint(s), possibly without any 
knowledge of the finger position (i.e., left index), the system, by searching 
through the database of available fingerprints associated with the known 
identities, will determine whether the print is associated with an identity.* 
The task of identity verification is much easier than that of identity recogni- 
tion: the former involving just one comparison while the latter involves 
multiple comparisons with fingerprints in the database. Although some civil- 
ian applications involve identity recognition, the underlying design consid- 
erations are different (see Figure 8.1). Despite these differences in the 
functionalities among different fingerprint identification application 
domains, all the fingerprint based systems rely on the distinctive individual 
information in fingerprints — the fingerprint expertise which has primarily 
resided within law enforcement agencies for more than a century. Further, 
the authors believe that law enforcement agencies will eventually also be 
closely involved in studying the civilian/commercial/financial fingerprint 
(and more generally biometric) applications as well. 

For any biometric measurement to be incorporated into a positive person 
identification system, it is necessary that such measurements be acceptable 
to society. Despite the criminal stigma associated with fingerprints, a recent 
CNN poll found that fingerprints rate high in social acceptability. 4 While 
acceptability is a complex (and mutable) phenomenon depending on con- 
founding factors including individual/institutional trust, religious and per- 
sonal beliefs/values, and culture, two system issues influence acceptability: 
system security 5 and individual privacy. 6,7 The security issues ensure that the 
intruders will neither be able to access the individual information/measure- 
ments (e.g., obtain fingerprint information) nor be able to pose as other 
individuals by electronically interjecting stale and fraudulently obtained bio- 
metrics measurements (e.g., surreptitiously lifted fingerprints from surfaces 
touched by the individuals) into the system. It is desirable that a personal 
identification system uses the biometric measurements exclusively for the 
purposes for which they were acquired. For example, it may be possible to 
glean information about the medical conditions of individuals from their 



* The term "identification" is used in this chapter either to refer to the general problem 
of identifying individuals (identification/recognition and authentication/verification) or to 
refer to the specific problem of identifying (recognizing) an individual from a database 
which involves one to many searches. We rely on the context to disambiguate the reference. 




Figure 8.2 Functional block diagram of an "automatic" fingerprint identifica- 
tion system. The dotted lines illustrate alternative paths. Some of the functional 
blocks (e.g., indexing) can be performed either by an expert or a computer. The 
feature editing and match verification tasks are performed by an expert. Typically, 
a fingerprint matcher passes a ranked list of 10 to 100 fingerprints for the match 
verification stage; a fingerprint expert browses the original fingerprint images (as 
opposed to their representations) to confirm/reject a candidate match. 

biometric measurements. Second, people are concerned about linkages: 
unauthorized usage of biometric measurements across different identifica- 
tion systems (e.g., criminal and civilian fingerprint identification systems) to 
link the identities of people and to gather/track individual information that 
may otherwise be unavailable. It is necessary to enforce systemwide mecha- 
nisms to ensure the usage of the biometric measurement for its proscribed 
intent. As novel applications of fingerprints (and other biometric identifiers) 
become more widespread, law enforcement agencies will be increasingly 
involved in resolving the frauds involving repudiation (e.g., users denying having 
accessed the system), coercion (e.g., users claiming to have been forced into the 
system), contamination (e.g., erroneous acquisition of biometrics identifier not 
associated with the intended user), and circumvention (e.g., unauthorized user 












illegitimately gaining access to the system). Consequently, agencies may not 
only be required to pass judgments about the identities related to biometric 
identifiers but also about the integrity of the systems and the validity of the 
biometric measurements. 



System Architecture 

A fingerprint identification system is an automatic pattern recognition system 
that consists of three fundamental stages: (1) data acquisition: the fingerprint 
to be recognized is sensed; (2) feature extraction: a machine representation 
(pattern) is extracted from the sensed image; and (3) decision-making: the 
representations derived from the sensed image are compared with a repre- 
sentation stored in the system. The comparison typically yields a matching 
score quantifying the similarity between the two representations. If the score 
is higher than a threshold (determined by the system operating point [see 
Figure 8.1]), the representations are determined to have originated from the 
same finger (s). In an identification system, multiple comparisons may be 
needed. Often, the stored representations in the database are partitioned into 
bins, based either on information extrinsic to the sensed input measurements 
(e.g., sex and age of the individual) or on information intrinsic to the sensed 
image (e.g., fingerprint class or type [see “Fingerprint Classification” sec- 
tion]). As a result, the input fingerprint need not be searched in the entire 
database, but only in the particular bin(s) of interest. 

Different systems may use different numbers of available fingerprints 
(multiple impressions of a single finger or single impressions of multiple 
fingers) for person identification. The feature extraction stage may involve 
manual override and editing by experts. Image enhancement may be used 
for poor-quality images (see “Fingerprint Enhancement” section). 



Challenges 

While significant progress has been made in automatic fingerprint identifi- 
cation, there are still a number of research issues that need to be addressed 
to improve system accuracy. Most of the shortcomings in the accuracy of an 
automatic fingerprint identification system can be attributed to the acquisi- 
tion process: 

Inconsistent Contact 

The act of sensing distorts the fingerprint. Determined by the pressure and 
contact of the finger on the glass platen, the three-dimensional shape of the 



finger gets mapped onto the two-dimensional surface of the glass platen. 
Because the finger is not a rigid object and because the process of projecting 
the finger surface onto the image acquisition surface is not precisely con- 
trolled, different impressions of a finger are related to each other by various 
transformations. The most problematic of these projections appears to be 
elastic distortions of the friction skin of the finger that displaces different 
portions of the finger (ever so slightly) by different magnitudes and in dif- 
ferent directions (see Figure 8.14). 

Non-uniform Contact 

The ridge structure of a finger would be completely captured if ridges belong- 
ing to the part of the finger being imaged are in complete physical/optical 
contact with the image acquisition surface and the valleys do not make any 
contact with the image acquisition surface (see Figure 8.6). However, the 
dryness of the skin, shallow/worn-out ridges (due to aging/genetics), skin dis- 
ease, sweat, dirt, and humidity in the air all confound the situation, resulting 
in a non-ideal contact situation. In the case of inked fingerprints, an additional 
factor may include inappropriate inking of the finger; this results in “noisy,” low- 
contrast images, which leads to either spurious or missing minutiae. 

Irreproducible Contact 

Manual work, accidents, etc. inflict injuries to the finger, thereby changing 
the ridge structure of the finger either permanently or semi-permanently. 
Further, each impression of a finger may possibly depict a different portion 
of its surface. This may introduce additional spurious fingerprint features. 

Feature Extraction Artifacts 

The feature extraction algorithm (see, for example, “Minutiae Feature Extrac- 
tion” section) is imperfect and introduces measurement errors. Various image 
processing operations might introduce inconsistent biases to perturb the 
location and orientation estimates of the reported fingerprint structures from 
their gray-scale counterparts. 

Sensing 

The act of sensing itself adds noise to the image. For example, in the live- 
scan fingerprint acquisition method, residues from the previous fingerprint 
capture may be left behind. A typical imaging system geometrically distorts 
the image of the object being sensed due to imperfect imaging conditions. 
In the Frustrated Total Internal Reflection sensing scheme (see “Fingerprint 
Sensing” section), for example, there may be a geometric distortion because 
the image plane is not parallel to the glass platen. 



Apart from the fingerprint acquisition and feature extraction issues, there 
are three major additional challenges. 10 Although a number of automatic 
fingerprint classification methods (see “Fingerprint Classification” section) 
have been proposed and some of them are used in operational systems, 
fingerprint classification still remains one of the most difficult problems for 
both humans and machines. Currently, the fingerprint classification frame- 
work is mainly intended for human experts; this may not be optimal for an 
automatic system. 

In designing any automatic pattern recognition system, an important 
issue is the performance assessment of the system: how to evaluate the per- 
formance of a given system or how to verify that a deployed system satisfies 
certain performance specifications. Unfortunately, the performance evalua- 
tion problem is far from well established. 

In the absence of a good fingerprint compression scheme, storing hun- 
dreds of millions of fingerprints is too expensive. The wavelet-based method, 
Wavelet/Scalar Quantization (WSQ), which has been proposed as the stan- 
dard for fingerprint compression, can compress a fingerprint image by a 
factor of 10 to 25 (see Figure 8. 3). 11,12 An algorithm that can reach an even 
higher compression ratio is an important research topic. 



Fingerprint Sensing 

Depending on whether the acquisition process is offline or online, a finger- 
print may be either (1) an inked fingerprint, (2) a latent fingerprint, or (3) 
a live-scan fingerprint. 

The term inked fingerprint is used to indicate that the fingerprint image 
is obtained from an impression of the finger on an intermediate medium 
such as paper. An example of a rolled inked fingerprint is shown in 
Figure 8.4a. Typically, the first step in capturing a rolled impression of a 
fingerprint is to place a few dabs of ink on a slab and roll it out smoothly 
with a roller until the slab is covered with a thin, even layer of ink. The finger 
is then rolled from one side of the nail to the other side over the inked slab, 
which inks the ridge patterns on top of the finer completely. After that, the 
finger is rolled on a piece of white paper so that the inked impression of the 
ridge pattern of the finger appears on the white paper. Rolled inked finger- 
prints impressed on paper can be electronically scanned into digital rolled 
fingerprints using optical scanners or video cameras. The rolled acquisition 
method has remained a standard technique for fingerprint acquisition for more 
than a 100 years. 2,16 Rolled inked fingerprints tend to have a large area of valid 
ridges and furrows, but have large deformations due to the inherent nature of 
the rolled acquisition process. Acquisition of rolled fingerprints is cumbersome, 
slow, and requires practice and skill. In the context of an automatic personal 





(c) 



Figure 8.3 Fingerprint compression: (a) an uncompressed fingerprint image; (b) 
portion of image in (a) compressed using a generic image compression algorithm, 
JPEG 13 ; and (c) portion of image in (a) compressed using Wavelet/Scalar Quanti- 
zation (WSQ), a compression algorithm specifically developed for compressing 
images. Both JPEG and WSQ use a compression ratio of 12.9; JPEG typically 
introduces bloclty artifacts and obliterates detailed information. See Reference 
14 for more detailed imagery. 

identification system, it is both infeasible and socially unacceptable to use the 
rolled inked method to acquire fingerprints in the operational phase, although 
it may be feasible to use the rolled inked method in the enrollment phase.* 
Another method of acquiring an inked impression is called a dab (see 
Figure 8.4b). In this method, the inked finger is simply impressed on the paper 
without rolling it from nail to nail. Obviously, the fingerprint dab images cover 
a smaller fingerprint pattern area, but there is a smaller distortion in the print. 



* For example, Master Card relies on inked impressions for enrollment. 







Figure 8.4 Comparison of different fingerprint impressions: (a) a rolled inked 
fingerprint (from NIST 4 database); (b) an inked dab fingerprint (from NIST 4 
database); (c) live-scan (dab) fingerprint (captured with a scanner manufactured 
by Digital Biometrics); (d) a latent fingerprint; (e) fingerprint captured using a 
solid-state sensor. (From Jain, A.K. and Pankanti, S., Handbook for Image and 
Video Processing, Bovik, A., Ed., ©Academic Press, April 2000.) 





In forensics, a special kind of inked fingerprints, called latent fingerprints, 
is of great interest. Constant perspiration exudation of sweat pores on fin- 
gerprint ridges and intermittent contact of fingers with other parts of the 
human body and various objects leave a film of moisture and/or grease on 
the surface of fingers. In touching an object (e.g., a glass), the film of moisture 
and/or grease may be transferred to the object and leave an impression of 
the ridges thereon. This type of fingerprint is called a latent fingerprint. 
Latent fingerprints are very important in forensics. Actually, a major task in 
forensic fingerprinting application is searching and reliably recording latent 
fingerprints, which is dealt with elsewhere in this book. An example of a 
latent fingerprint is shown in Figure 8.4d. 

The live-scan fingerprint is a collective term for a fingerprint image 
obtained directly from the finger without the intermediate step of getting an 
impression on paper. A live-scan fingerprint is usually obtained using the 
dab-method, in which a finger is impressed on the acquisition surface of a 
device without rolling.* A number of sensing mechanisms can be used to 
sense the ridge and furrows of the finger impressions, including (1) optical 
frustrated total internal reflection (FTIR), 17-19 (2) ultrasonic reflection, 20-22 
(3) optical total internal reflection of holograms, 23-25 ( 4) thermal sensing of 
the temperature differential (across the ridges and valleys), 26,27 (5) sensing of 
differential capacitance (across the ridges and valleys), 28-31 and (6) non-con- 
tact 2-D or non-contact 3-D scanning. 32,33 Scanners based on these physical 
processes can be used to acquire the fingerprint impressions directly and 
these acquisition methods eliminate the intermediate digitization process of 
inked impressions and enable the design of online verification systems. 
Depending on the clarity of ridge structures of scanned fingers and acquisi- 
tion conditions, live-scan fingerprints vary in quality. Because of the online 
nature of this acquisition method, it is possible to directly observe the print 
being acquired; such a visual feedback turns out to be the single most impor- 
tant factor in controlling the quality of acquired fingerprints. 

The most popular technology to obtain a live-scan fingerprint image is 
based on the optical frustrated total internal reflection (FTIR) concept. 17 
When a finger is placed on one side of a glass platen (prism), ridges of the 
finger are in contact with the platen, while the valleys of the finger are not 
in contact with the platen. The remainder of the imaging system essentially 
consists of an assembly of an LED light source and a CCD camera placed on 
the other side of the glass platen. The laser light source illuminates the glass 
at a certain angle and the camera is placed such that it can capture the laser 
light reflected from the glass. The light that is incident on the plate at the 



* It is also possible to capture a rolled live-scan fingerprint. Some vendors use elaborate 
software and/or scanner arrangements to capture rolled fingerprint live-scan images from 
one or more live-scan dabs. 




Figure 8.5 FTIR fingerprint scanner manufactured by Digital Biometrics. (From 
Digital Biometrics, Digital Biometrics Homepage, http://www.digitalbiomet- 
rics.com/. With permission.) 

glass surface touched by the ridges is randomly scattered, while the light 
incident at the glass surface corresponding to valleys suffers total internal 
reflection, resulting in a corresponding fingerprint image on the imaging 
plane of the CCD. An example of a live-scan fingerprint is shown in 
Figure 8.4c. Figure 8.5 shows an FTIR fingerprint scanner and Figure 8.6 
depicts the sensing mechanism. Typically, an optical live-scan fingerprint 
scanner images span an area that is approximately 0.75 in. 2 . There are vendors 
that supply optical scanners which are also capable of imaging very large 
areas of friction skin and facilitate ten-print or palmprint/soleprint scanning 
(see, for example, References 32 and 35). 

The other live-scan modalities of fingerprint acquisition strive to 
(1) reduce the size/price of the optical scanning system, (2) improve the 
quality/resolution of the prints, and/or (3) improve the geometric/photo- 
metric/elastic distortion characteristics involved in the image capture. For 
example, by scanning the internal layers of friction skin (as opposed to 
scanning the superficial surface layers of the friction skin), an ultrasound 
method of fingerprint imaging is believed to be capable of acquiring a very 
clear fingerprint image even if the impressed finger does not apparently have 
clear ridge structures. Imaging in a typical FTIR optical scanner suffers from 
geometric distortion because the fingerprint surface (platen) is not parallel 
to the imaging surface. Hologram-based live scans avoid this problem and 
hence the resulting fingerprint images are believed to have better spatial 
fidelity. Further, the edge-lit holograms 23 avoid bulky illumination optics 
and are thus compact. Some hologram-based scanners have demonstrated 



L 



(a) 



Finger Friction Surface 




Figure 8.6 Optical fingerprint sensing, (a) Imaging geometry consists of a laser 
source (L) illuminating a finger resting on a glass platen/prism (P) and an imaging 
surface (C). (b) Frustrated total internal reflection: the ray A incident at the 
ridge/glass interface scatters while the ray B falling at the valley/glass interface 
suffers total internal reflection and the reflected rays are collected at the imaging 
surface. 




Figure 8.7 Solid-state fingerprint chips, (a) Differential capacitance fingerprint 
chip manufactured by Veridicom. (From Veridicom. Veridicom Homepage. 
http://www.veridicom.com/.) (b) A capacitance-based fingerprint imaging mouse 
made by Siemens. (Siemens. The ID Mouse from Siemens, http://www.fingertip.de/.) 



1000 dpi resolution 36 in laboratory settings. Thomson CSF manufactures a 
“sweep” -based fingerprint scanner based on thermal sensing; this scheme claims 
to have significantly better reliability in harsh environmental conditions and a 
large imaging area. The contact-less scanners permit imaging without contact 
and hence eliminate the problems related to elastic distortion in the finger- 
prints caused by contact with the presentation surface. Optical scanners are 
too large to be readily integrated in a number of applications such as laptop 
security, cellular phone security, and notebook security. Recently, a number 
of different types of compact solid-state fingerprint chips have become avail- 
able. These solid-state chips can be manufactured at very low cost if made 
in large quantities. Figure 8.7 shows two commercially available solid-state 
fingerprint chips. 

Tive-scan fingerprinting is an emerging technology and it is too early to 
assess its strengths based on the existing commercial products. At this 
moment, with respect to imaging area, gray-scale resolution, and spatial 
resolution, (rolled) inked fingerprints appear to be superior to the optical 
live-scans; optical FTIR live-scans are superior to solid-state fingerprints 
sensors. The forensic community has extensively evaluated the quality of live- 
scan fingerprints and expressed concerns about quality of fingerprints acquired 
using live-scan fingerprint sensors. In its quest to establish minimum require- 
ments for fingerprint acquisition for criminal applications, various U.S. Gov- 
ernment agencies have compiled compliance specifications for the optical live- 
scan fingerprints (see, for example, image quality specifications (IQS). 38,39 





Fingerprint Representation 



A fingerprint is a smoothly flowing pattern of alternating valleys and ridges, 
the ridges and valleys being parallel in most regions. Several permanent and 
semi-permanent features such as scars, cuts, bruises, cracks, and calluses are 
also present in a fingerprint. 

What information is available in fingerprints to enable sound judgment 
about whether two prints have originated from the same finger or from 
two distinct fingers? To reliably establish whether two prints came from 
the same finger or different fingers, it is necessary to capture some invariant 
representation (features) of the fingerprints: the features which over a life- 
time will continue to remain relatively unaltered irrespective of the cuts and 
bruises, the orientation of the finger placement with respect to the medium 
of the capture, occlusion of a small part of the finger, the imaging technology 
used to acquire the fingerprint from the finger, or the elastic distortion of 
the finger during the acquisition of the print. 

Several representations have been used to assess fingerprint similarity. 
Fingerprint representations can be broadly categorized into two types: global 
and local. A global representation is an overall attribute of the finger and a 
single representation is valid for the entire fingerprint and is typically deter- 
mined by an examination of the entire finger. A local representation consists of 
several components, each component typically derived from a spatially 
restricted region of the fingerprint. Typically, global representations are used for 
fingerprint indexing and local representations are used for fingerprint matching. 

One of the significant global features used for fingerprints is its class or 
type. The overall fingerprint pattern is typically categorized into a small 
number of classes. Several fingerprint classification schema exist and, as 
mentioned earlier, we will avoid delving into the details of the classifications 
schema adopted by different automatic identification systems. A typical fin- 
gerprint classification scheme categorizes the prints into the following six 
major classes: whorl, right loop, left loop, arch, twin loop, and tented arch 
(see Figure 8.8).* Sometimes, a synthetic category called scars is included to 
classify fingerprints mutilated with scars, thus obscuring the possibility of 
accurately determining its true class. 

Fingers can also be distinguished based on features such as ridge thick- 
ness, ridge separation, or ridge depths. Some examples of global representa- 
tion include information about locations of critical points (e.g., core and 
delta) in a fingerprint. Core-delta ridge count feature, sometimes simply 
referred to as the ridge count, measures the number of ridges between core 



* A typical AFIS may use the following eight classes: (1) whorl, (2) radial loop, (3) ulnar 
loop, (4) double loop, (5) arch, (6) tented arch, (7) accidental, and (8) central pocket loop. 



and delta points (see Figure 8.8) on a finger.* All these features measure an 
overall property of a finger and these similarities are referred to as global or 
generic features. 

Major representations of the local information in fingerprints are based 
on finger ridges, pores on the ridges, or salient features derived from the 
ridges. Sometimes, the entire fingerprint itself (or some condensed form of 
it) is used as the fingerprint representation. 40,41 The most widely used local 
features are based on minute details (minutiae) of the ridges (Figures 8.9 and 
8.10). The pattern of the minute details of a fingerprint forms a valid repre- 
sentation of the fingerprint. This representation is compact and captures a 
significant component of individual information in fingerprints; compared 
to other representations, minutiae extraction is relatively more robust to various 
sources of fingerprint degradation. Most types of minute details in fingerprint 
images are not stable and cannot be reliably identified by automatic image 
processing methods. Therefore, in automatic fingerprint matching, only the 
two most prominent types of minute details are used for their stability and 
robustness: (1) ridge ending and (2) ridge bifurcation. In addition, because 
various data acquisition conditions such as impression pressure can easily 
change one type of minutiae into the other, typical minutiae-based repre- 
sentations do not make any distinction between these two types of features 
and are collectively referred to as minutiae. The simplest of the minutiae- 
based representations constitute a list of points defined by their spatial coor- 
dinates with respect to a fixed image-centric coordinate system. Typically, 
however, these minimal minutiae-based representations are further enhanced 
by tagging each minutiae (or each combination of minutiae subset, e.g., pairs, 
triplets) with additional features. For example, each minutiae could be asso- 
ciated with the orientation of the ridge at that minutiae; or each pair of the 
minutiae could be associated with the ridge count, which is the number of 
ridges visited during the linear traversal between the two minutiae. The 
ANSI-NIST standard representation of a fingerprint is predominantly based 
on minutiae and includes one or more global attributes such as orientation 
of the finger, locations or core or delta,** and fingerprint class. Typically, in 
a live-scan fingerprint image of good quality, there are approximately 40 to 
60 minutiae (in a typical 512x512 image). 

Another local fingerprint feature is sweat pore information. The location 
and densities of the minute sweat pores have been found to contain infor- 
mation helpful in distinguishing individuals. 36 



* Some categories of fingerprints do not intrinsically have any core or delta. In such cases, 
an automatic system may in some consistent way define other landmark features of 
fingerprints in lieu of core-delta ridge count, core, and/or delta. 

* * Core and delta are the two distinctive global structures in a fingerprint. 2 See Figure 8.8c. 




Figure 8.8 A fingerprint classification schema involving six categories: (a) arch, 
(b) tented arch, (c) right loop, (d) left loop, (e) whorl, and (f) twin loop. Critical 
points in a fingerprint, called core and delta, are marked as squares and triangles, 
respectively. An arch does not have a delta or a core. One of the two deltas in 
(e) and both deltas in (f) are not imaged. A sample minutiae ridge ending (o) and 
ridge bifurcation (x) are illustrated in (e). Each image is 512 x 512 with 256 gray 
levels and is scanned at 512 dpi resolution. (From Jain, A., Hong, L., Pankanti, 
S., and Bolle, R., On-line identity-authentication system using fingerprints. Proc. 
IEEE (Special Issue on Automated Biometrics), 85(9), 1365-1388, ©IEEE, Sep- 
tember 1997.) 

The guidelines for (visual) matching of fingerprints are quite elaborate. 
A fingerprint expert often relies on subtle and complex reasoning to argue 
whether two prints originated from a single finger or two distinct fingers. 
For example, an expert can visually localize several rich features of a finger- 
print with remarkable accuracy. These features include the locations of core, 
delta, islands, dots, short ridges, ridge endings, ridge bifurcations, and numerical 





(e) (f) 



Figure 8.8 (continued) 




Figure 8.9 Schematic representation of a ridge ending (E) and a ridge bifurca- 
tion/branching (B). A minutiae is typically quantified by its (x, y) coordinates and 
the orientation of the abutting ridge. Different representation conventions are 
used by different automatic fingerprint identification systems. 

values of orientation of the ridges, and number of ridges between two features 
(ridge counts). An expert can reliably use judgments about scars, complex visual 
textures, sweat pores, and ridge thickness to rule out false matches. It is not an 
exaggeration to state that research in automatic fingerprint identification has 
been mostly an exercise in imitating the performance of a human fingerprint 





Figure 8.10 Relative configuration of ridge endings and branchings between two 
impressions of the same finger. The minutiae were extracted using the algorithm 
in Reference 9 and the correspondences were manually determined for illustration. 

expert without access to the many underlying information-rich features an 
expert is able to glean from visual examination. The lack of such a rich set 
of informative features in automatic systems is primarily due to the unavail- 
ability of complex modeling techniques and image processing techniques that 
can reliably and consistently extract detailed features in the presence of noise. 

It should be noted that, at least in the context of law enforcement/forensic 
applications of fingerprint-based identification, the machine representations 
alone are not considered a sufficient basis for assessing the matching outcome 
and other visual features of the original fingerprint can sway the final decision. 
Although there are FBI recommendations about the minimum number of 
corresponding minutiae for declaring a “fingerprint match,” a fingerprint 
expert can overrule such recommendations based on his/her visual judgment. 
For an illustration of the danger in exclusively relying on parsimonious 
representations such as minutiae, see Reference 43. 

Considering the relative simplicity of the automatically extracted finger- 
print representations and the brittleness of the processing algorithms, espe- 
cially in the context of poor quality fingerprints, an expert is actively involved 
in the processing/ classification/ matching stages of a typical fingerprint iden- 
tification system, especially in forensic applications. 

Minutiae Feature Extraction 



This chapter section summarizes a typical automatic feature extraction algo- 
rithm for minutiae representation. An outline of feature extraction related 





Input Image 




Minutiae Points 



Thinned Ridges 






Figure 8.11 Flowchart of the minutiae extraction algorithm. (From Jain, A., 
Hong, L., Pankanti, S., and Bolle, R., On-line identity-authentication system using 
fingerprints, Proc. IEEE (Special Issue on Automated Biometrics), 85(9), 
1365-1388, September 1997.) 



to fingerprint classification is presented in the next chapter section, while 
detailed exposition of these algorithms is presented in References 9 and 10. 
Computation of fingerprint quality estimation and fingerprint ridge count 
is not presented here due to space limitation and readers are referred to 
typical algorithms presented elsewhere in the literature. 44,45 

The overall flowchart of a typical minutiae extraction algorithm is 
depicted in Figure 8.11. This particular method of minutiae extraction con- 
sists mainly of three stages: (1) orientation field estimation, (2) ridge extrac- 
tion, and (3) minutiae extraction and post-processing. First, for an input 
image, the local ridge orientation is estimated and the region of interest is 
located. Then, ridges are extracted from the input image, refined to get rid 
of the small speckles and holes, and thinned to obtain eight connected single- 
pixel-wide ridges. Finally, minutiae are extracted from the thinned ridges and 
refined using some heuristics. We assume that the resolution of input finger- 
print images is 500 dpi, which is the recommended resolution for automatic 
fingerprint identification by the FBI. 





A minutiae feature extractor finds the ridge endings and ridge bifurca- 
tions from the input fingerprint images. If ridges can be perfectly located in 
an input fingerprint image, then minutiae extraction is a relatively simple 
task of extracting singular points in a thinned ridge map. However, in prac- 
tice, it is not always possible to obtain a perfect ridge map. The performance 
of currently available minutiae extraction algorithms depends heavily on the 
quality of the input fingerprint images. Due to a number of factors (aberrant 
formations of epidermal ridges of fingerprints, postnatal marks, occupational 
marks, problems with acquisition devices, etc.), fingerprint images may not 
always have well-defined ridge structures. 

Orientation Estimation 

A gray-level fingerprint image, I, is defined as an N x N matrix, where I(i,j ) 
represents the intensity of the pixel at the z th row and j' h column. Typically, 
fingerprints are 8-bit gray-level images and a pixel grey level in a fingerprint 
can nominally range from 0 to 255. The actual gray levels in a fingerprint 
may span significantly smaller range either due to (1) poor finger contact 
with the sensor, (2) poor imaging, or (3) shallow ridges/valleys. Many systems 
first preprocess the fingerprint images before subjecting them to the process- 
ing steps described below. This preprocessing might typically consist of either 
gray-level smoothing, contrast stretching, and/or spatial/frequency domain 
filtering. In extreme cases, a very poor fingerprint can be automatically 
enhanced (see “Fingerprint Enhancement” section). 

An orientation field/image is defined as an N x N image, where 0(i, j ) 
represents the local ridge orientation at pixel ( i,j ). The local ridge orientation 
cannot be meaningfully determined from the gray value at pixel ( i,j ) alone; 
it is typically computed from pixels of the surrounding (rectangular block) 
region. An image is divided into a set of w x w nonoverlapping blocks and 
a single local ridge orientation is defined for each block. Typically, w is deter- 
mined by the image resolution and magnitude of w is comparable to one to two 
inter-ridge distances (e.g., 32 x 32 pixels in a 512-dpi fingerprint image). 

One approach to ridge orientation estimation relies on local image gra- 
dient. A gray-scale gradient is a vector whose orientation indicates the direc- 
tion of the steepest change in the gray values and whose magnitude depends 
on the amount of change of the gray values in the direction of the gradient. 
The local orientation in a block can be determined from the constituent pixel 
gradient orientations of the block in several ways. For example, one could 
determine the block gradient orientation by averaging the pixel gradient 
orientations. 46 An alternative method of determining block gradient orien- 
tation relies on a voting scheme involving pixel gradient orientations. 47 
Another method 48 uses a least-square optimization scheme involving the 
pixel gradient orientations. 




The rationale for determining a single orientation for each block of w x 
w pixels (rather than for each pixel) is computational efficiency. Conse- 
quently, in regions of a fingerprint with smoothly flowing parallel ridges, 
representing a single ridge orientation for an entire block is not unreasonable, 
but in the regions where the ridges are sharply changing their directions (e.g., 
regions surrounding core or delta) or the regions with cuts/scars, the choice 
of local ridge direction per block is ambiguous. Note that in a fingerprint 
image, the ridges oriented at 0° and the ridges at 180° in a local neighborhood 
cannot be differentiated from each other. 

Segmentation 

The objective of this stage is to locate the actual region in the fingerprint 
image depicting the finger (region of interest) and discard the regions of the 
image containing irrelevant information (e.g., dirt, smudges leftover from 
previous acquisitions, and spurious [pencil] markings in inked impressions). 
This stage is also sometimes referred to as foreground/background detection. 
Note that this stage is not responsible for discriminating the ridges against 
valleys. A typical approach to segmentation might involve smearing (spatial 
gray-scale smoothing) the fingerprint image and using fixed/adaptive thresh- 
olding to discard background region. This approach can produce reasonable 
results for a good-quality print but may not easily remove the extraneous 
artifacts in a poor-quality fingerprint image. A method of segmentation based 
on the concept of certainty level of orientation field estimation is described 
here. 

After the orientation field of an input fingerprint image is estimated, a 
region of interest localization algorithm, which is based on the local certainty 
level of the orientation field, is used to locate the region of interest within 
the input image. The certainty level of the orientation field in a block quan- 
tifies the extent to which the pixel gradient orientations agree with the block 
gradient orientation. For each block, if the certainty level of the orientation 
field is below a threshold, then all the pixels in this block are marked as 
background pixels. Because the computation of certainty level is a by-product 
of the local ridge orientation estimation, it is a computationally efficient 
approach. The authors have found that this method of segmentation per- 
forms reasonably well in detecting the region of interest. 

Ridge Detection 

As alluded earlier, the objective of the ridge detection algorithm is to separate 
ridges from valleys in a given fingerprint image. Previous approaches to ridge 
detection have used either global or adaptive thresholding, that is, pixels 
darker/brighter than a constant/variable threshold are determined to be pixels 




depicting a ridge in the fingerprint. These straightforward approaches gen- 
erally do not work well for noisy and low-contrast portions of the image. 

A more reliable property of the ridges in a fingerprint image is that the 
gray-level values on ridges attain their local minima* along a direction nor- 
mal to the local ridge orientation. 9,48 Pixels can be identified to be ridge pixels 
based on this property. Given the local ridge orientation at a pixel ( i, j) in 
the foreground portion of the image, a simple test can be devised to deter- 
mine whether the gray-level values in the fingerprint image attain a local 
minima at (i, j) along a direction normal to the ridge orientation. The 
resultant image is a binary image; for example, the loci of the minima are 
marked 1 and all other pixels are marked 0. The ridges thus detected are 
typically thick (e.g., 3 pixels wide) and standard thinning algorithms 49 can 
be used to obtain 1 -pixel thin ridges. Thinned ridges facilitate the detection 
of minutiae. Before applying a thinning algorithm, spurious structures (e.g., 
dirt) detected as ridges must be discarded based on their (small) area. 

Minutiae Detection 

Once the thinned ridge map is available, the ridge pixels with three-ridge 
pixel neighbors are identified as ridge bifurcations and those with one-ridge 
pixel neighbor are identified as ridge endings. However, all the minutiae thus 
detected are not genuine due to image processing artifacts and the noise 
present in the fingerprint image. 

Post-processing 

In this stage, typically, genuine minutiae are gleaned from the extracted 
minutiae using a number of heuristics. For example, too many minutiae in 
a small neighborhood may indicate the presence of noise and they could be 
discarded. Very close ridge endings that are oriented anti-parallel to each 
other may indicate spurious minutiae generated by a break in the ridge due 
either to poor contrast or a cut in the finger. Two very closely located bifur- 
cations sharing a common short ridge often suggest extraneous minutiae 
generated by bridging of adjacent ridges as a result of dirt or image processing 
artifacts. 



Fingerprint Classification 

Fingerprints have been traditionally classified into categories based on the infor- 
mation contained in the global patterns of ridges. In large-scale fingerprint 
identification systems, elaborate methods of manual fingerprint classification 



* In a fingerprint image where ridges are darker than valleys. 





systems were developed to index individuals into bins based on classification 
of their fingerprints. These methods of binning eliminate the need to match 
an input fingerprint to the entire fingerprint database in identification appli- 
cations, thereby significantly reducing the computing requirements. 50 ' 52 

Efforts in automatic fingerprint classification have been exclusively 
directed at replicating the manual fingerprint classification system. Figure 8.8 
shows one prevalent manual fingerprint classification scheme that has been 
the focus of many automatic fingerprint classification efforts. It is important 
to note that the distribution of fingers into the six classes (shown in 
Figure 8.8) is highly skewed (32.5% left loop, 32.5% right loop, 30% whorl, 
5% other). A fingerprint classification system should be invariant to rotation, 
translation, and elastic distortion of the frictional skin. In addition, often a 
significant part of the finger may not be imaged (e.g., dabs frequently miss 
deltas) and the classification methods requiring information from the entire 
fingerprint may be too restrictive for many applications. 

A number of approaches to fingerprint classification have been devel- 
oped. Some of the earliest approaches did not make use of the rich informa- 
tion in the ridge structures and exclusively depended on orientation field 
information. Although fingerprint landmarks provide very effective finger- 
print class clues, methods relying on the fingerprint landmarks alone may 
not be very successful due to lack of availability of such information in many 
fingerprint images and to the difficulty in extracting the landmark informa- 
tion from the noisy fingerprint images. As a result, a successful approach needs 
to (1) supplement the orientation field information with ridge information; (2) 
use fingerprint landmark information when available, but devise alternative 
schemes when such information cannot be extracted from the input fingerprint 
images; and (3) use structural/syntactic pattern recognition methods in addition 
to statistical methods. We summarize a method of classification 10 that takes into 
consideration the above-mentioned design criteria that has been tested on a 
large database of realistic fingerprints to classify fingers into five major catego- 
ries: right loop, left loop, arch, tented arch, and whorl*. 

The orientation field determined from the input image may not be very 
accurate and the extracted ridges may contain many artifacts and, therefore, 
cannot be directly used for fingerprint classification. A ridge verification stage 
assesses the reliability of the extracted ridges based on the length of each 
connected ridge segment and its alignment with other adjacent ridges. Par- 
allel adjacent subsegments typically indicate a good-quality fingerprint 
region; the ridge/orientation estimates in these regions are used to refine the 
estimates in the orientation field/ridge map. 



* Other types of prints (e.g., twin-loop) are not considered here but, in principle, could be 
lumped into "other" or "reject" category. 



1. Singular points. The Poincare index 46 computed from the orientation 
field is used to determine the number of delta (N d ) and core (N c ) points 
in the fingerprint. A digital closed curve, \|/, about 25 pixels long, around 
each pixel is used to compute the Poincare index as defined below. 

Given a fingerprint orientation field, the Poincare index at a pixel 
( i,j ) is the integration (summation) of all differences in orientations 
of successive pixels along a square shaped curve centered around pixel 
( z, j) . The Poincare index at most of the pixels in a fingerprint image 
is equal to zero and these points are called non-singular points. The 
pixels with non-zero Poincare index always take a value of 1/2 or -1/2 
and are called singular points. The Poincare index of a core-shaped 
singular point has a value of 1/2, and the Poincare index of a delta- 
shaped singular point has a value of -1/2. 

The size of the square used for computing the Poincare index is 
crucial for the performance of a singular point detection algorithm. 
If it is too small, then a small perturbation of orientations may result 
in spurious singular points being detected. On the other hand, if it is 
too large, then a true pair of core and delta which are close to one 
another can be ignored because the Poincare index of a digital curve 
that includes an equal number of cores and deltas is 0. For a 512-dpi 
fingerprint image, for example, a square curve with a length of 25 
pixels can be used for computation of the Poincare index. The results 
of the Poincare index cannot be directly used to obtain core/delta point 
locations and may need some post-processing. 10 

2. Symmetry. The feature extraction stage also estimates an axis that is 
locally symmetric to the ridge structures at the core and computes (1) 
a, the angle between the symmetry axis and the line segment joining 
core and delta, (2) (3, the average angle difference between the ridge 
orientation and the orientation of the line segment joining the core 
and delta, and (3) y, the number of ridges crossing the line segment 
joining core and delta. The relative position, R, of delta with respect 
to the symmetry axis is determined as follows: R = 1 if the delta is on 
the right side of symmetry axis, R = 0 otherwise. 

3. Ridge structure. The classifier not only uses the orientation information 
but also utilizes the structural information in the extracted ridges. This 
feature summarizes the overall nature of the ridge flow in the fingerprint. 
In particular, it classifies each ridge of the fingerprint into three categories: 

• Non-recurving ridges: the ridges that do not curve very much 

• Type- 1 recurving ridges: ridges that curve approximately n 

• Type-2 fully recurving ridges: ridges that curve by more than it 

The classification algorithm summarized here (see Figure 8.12) essen- 
tially devises a sequence of tests for determining the class of a fingerprint 



whorl tented arch left loop 




Figure 8.12 Flowchart of fingerprint classification algorithm. Inset also illus- 
trates ridge classification. The "re-compute" option involves starting the classi- 
fication algorithm with a different preprocessing (e.g., smoothing) of the image. 
(From Hong, L. ( Automatic Personal Identification Using Fingerprints, Ph.D. 
thesis, Michigan State University, 1998. With permission. Jain, A.K. and Pan- 
kanti, S. Fingerprint classification and matching, in A. Bovik, Ed., Handbook for 
Image and Video Processing, ©Academic Press, April 2000. With permission.) 

and conducts simpler tests near the root of the decision tree. For example, 
two core points are typically detected for a whorl (see Figure 8.12, which is 
an easier condition to verify than detecting the number of Type-2 recurving 
ridges.) Another highlight of the algorithm is that if it cannot detect the 
salient characteristics of any category from the features extracted in a finger- 
print, it re-computes the features with a different pre-processing method. 
For example, in the current implementation, the differential pre-processing 
consists of a different method/scale of smoothing the image. As can be 
observed from the flowchart, the algorithm detects (1) whorls based upon 
detection of either two core points or a sufficient number of Type 2-recurving 
ridges; (2) arch based upon the inability to detect either delta or core points; 
(3) left (right) loops based on the characteristic tilt of the symmetric axis, 
detection of a core point, and detection of either a delta point or a sufficient 
number of Type- 1 recurving ridges; and (4) tented arch based on the presence 
of a relatively upright symmetric axis, detection of a core point, and detection 
of either a delta point or a sufficient number of Type-1 recurving ridges. 



Table 8.2 Five-Class Classification Results 
on the NIST-4 Database; A = Arch, T = Tented 
Arch, L = Left Loop, R = Right Loop, W = Whorl 



True Class 




Assigned Class 




A 


T 


L 


R 


W 


A 


885 


13 


10 


11 


0 


T 


179 


384 


54 


14 


5 


L 


31 


27 


755 


3 


20 


R 


30 


47 


3 


717 


16 


W 


6 


1 


15 


15 


759 



From Jain, A.K. and Pankanti, S. Fingerprint classification and 
matching, in A. Bovik, Ed., Handbook for Image and Video 
Processing, ©Academic Press, April 2000. With permission. 



Table 8.2 shows the results of the fingerprint classification algorithm on 
the NIST-4 database which contains 4000 images (image size is 512 x 480) 
taken from 2000 different fingers, 2 images per finger. Five fingerprint classes 
are defined: (1) arch, (2) tented arch, (3) left loop, (4) right loop, and (5) 
whorl. Fingerprints in this database are uniformly distributed among these 
five classes (800 per class). The five-class error rate in classifying these 4000 
fingerprints is 12.5%. The confusion matrix is given in Table 8.2; numbers 
shown in bold font are correct classifications. Because a number of finger- 
prints in the NIST-4 database are labeled as belonging to possibly more than 
one class, each row of the confusion matrix in Table 8.2 does not sum up to 
800. For the five-class problem, most of the classification errors are due to 
misclassifying a tented arch as an arch. By combining these two categories into 
a single class, the four-class error rate drops from 12.5% to 7.7%. In addition 
to the tented arch-arch errors, the errors primarily result from misclassifications 
between arch/tented arch and loops and from poor image quality. 



Fingerprint Matching 

Given two (test and template) representations, the matching module deter- 
mines whether the prints are impressions of the same finger. The matching 
phase typically defines a metric of the similarity between two fingerprint 
representations. It also defines a threshold to decide whether or not a given 
pair of representations belongs to the same finger (mated pair). 

Only in the highly constrained systems (see, for example, Reference 41) and 
situations could one assume that the test and template fingerprints depict the 
same portion of the finger and that both are aligned (in terms of displacement 
from the origin of the imaging coordinate system and of their orientations) with 



each other. Thus, in typical situations, one needs to (either, implicitly or explic- 
itly) align (or register) the fingerprints (or their representations) before deciding 
whether the prints are mated pairs. Further, there are two additional chal- 
lenges involved in determining the correspondence between two aligned finger- 
print representations (see Figure 8.13): (1) dirt/leftover smudges on the sensing 
device and the presence of scratches/cuts on the finger either introduce spurious 
minutiae or obliterate the genuine minutiae; and (2) variations in the area of 
finger being imaged and its pressure on the sensing device affect the number of 
genuine minutiae captured and introduce displacement of the minutiae from 
their “true” locations due to elastic distortion of the fingerprint skin. Such elastic 
distortions and feature extraction artifacts account for minutiae matching errors 
even after the prints are in the best possible alignment. 

A typical strategy for fingerprint matching is to first align the fingerprint 
representations and then examine the prints for corresponding structures in the 
aligned representations. Because solutions to both the problems (alignment and 
correspondence) are interrelated, they are (implicitly) solved simultaneously. 

A number of strategies have been employed in the literature to solve the 
alignment problem. Typically, it is assumed that the alignment of the test and 
template fingerprints involves an overall displacement (translation) and rota- 
tion. The scale variations, shear transformations, and local elastic deformations 
are often overlooked in the alignment stage. In image-based representations, the 
alignment of the prints can be obtained by optimizing their image correlation. 
In ridge representations of the fingerprints, portions of ridges can be used to 
align the prints. 9 In minutiae-based representations, the alignment process typ- 
ically uses predominantly minutiae positions; minutiae angles are not signifi- 
cantly involved because they are vulnerable to image noise/distortion. Other 
supplementary information (e.g., connectivity, nearest neighboring minutiae, 
ridge count) can often participate in the alignment process. In minutiae-based 
alignment, a single minutia, pairs of minutiae, or triplets of minutiae have been 
used to hypothesize an alignment. In Reference 48, for example, all possible test 
and template minutiae pair correspondence possibilities are exhaustively con- 
sidered; each hypothesized pairing votes for all feasible translations and rota- 
tions. In Reference 51, an input minutia triplet votes for a feasible 
transformation to congruent template triplet. The transformation receiving the 
maximum number of votes is deemed to be the best transformation. 

Once the prints are aligned, the corresponding structures in the aligned 
representations provide the basis for computing the matching score. In image- 
based representation, the correlation coefficient generated during the align- 
ment can serve as a matching score. The elastic deformation, shear transforma- 
tion, and scale variations may impose severe limitations on the utility of image 
correlation and image-based representations. In an elastic minutia-based 




(b) 

Figure 8.13 Two different impressions of the same finger. To know the corre- 
spondence between the minutiae of these two fingerprint images, all minutiae 
must be precisely localized and the deformations must be recovered. 




Figure 8.14 Aligned ridge structures of mated pairs. Note that the best align- 
ment in one part (center) of the image results in large displacements between 
the corresponding minutiae in the other regions (bottom right). (From Jain, A., 
Hong, L., Pankanti, S., and Bolle, R., On-line identity-authentication system using 
fingerprints, Pioc. IEEE (Special Issue on Automated Biometrics), 85(9), 
1365-1388, September 1997.) 

matching, the test minutiae are searched in a square region centered (bound- 
ing box) around each template minutia in the aligned representation. The 
elastic matchers account for small local elastic deformations. 

Figure 8.14 illustrates a typical situation of aligned ridge structures of 
mated pairs. Note that the best alignment in one part (center) of the image 
can result in a large amount of displacement between the corresponding 
minutiae in the other regions (bottom right). In addition, observe that the 
distortion is nonlinear: given distortions at two arbitrary locations on the 
finger, it is not possible to predict the distortion at all the intervening points 
on the line joining the two points. Accommodating such large nonlinear 
distortions was the motivation underlying the design of the adaptive elastic 
string matching algorithm. 9 

The operation of the adaptive elastic string matching algorithm (string 
matcher, for short) is similar to an elastic matcher. As in an elastic matcher, the 
test minutiae are searched in the bounding box neighborhood of each template 
minutia. In the string matcher, however, the size of the bounding box around 
each template minutia, unlike in elastic matcher, is not constant. The bounding 



box size is adjusted based on the estimate of the local deformation; the estimate 
of the local deformation is derived from the bounding boxes of the already 
matched minutia in the neighborhood of the current template minutiae. 

The string matcher first selects a pair of corresponding minutiae in test 
and template representations based on information associated with an 
adjoining portion of ridge; the minutiae sets in this pair of minutiae are 
called the reference test and reference template minutiae. The string matcher 
uses three attributes of the aligned minutiae for matching: its distance from 
the reference minutiae (radius), angle subtended to the reference minutiae 
(radial angle), and local direction of the associated ridge (minutiae direction). 
The algorithm initiates the matching by first representing the aligned input 
(template) minutiae as an input (template) minutiae string. The string rep- 
resentation is obtained by imposing a linear ordering on the minutiae using 
radial angles and radii. The resulting input and template minutiae strings 
are matched using an inexact string matching algorithm to establish the 
correspondence. 

The inexact string matching algorithm essentially transforms (edits) the 
input string to template string and the number of edit operations is used to 
define the (dis) similarity between the strings. While permitted edit operators 
model the fingerprint impression variations (deletion of the genuine minu- 
tiae, insertion of spurious minutiae, and perturbation of the minutiae), the 
penalty associated with each edit operator reflects the likelihood of that edit 
operation. The sum of penalties of all the edits (edit distance) defines the 
similarity between the input and template minutiae strings. Among several 
possible sets of edits that permit the transformation of the input minutiae 
string into the reference minutiae string, the string matching algorithm 
chooses the transform associated with the minimum cost using dynamic 
programming. 

The algorithm tentatively considers a candidate (aligned) input and a 
candidate template minutiae to be a mismatch if their attributes are not 
within a tolerance window (see Figure 8.15) and penalizes them for the 
deletion/insertion edit operation. If the attributes are within the tolerance 
window, the amount of penalty associated with the tentative match is pro- 
portional to the disparity in the values of the attributes in the minutiae. The 
algorithm accommodates for the elastic distortion by adaptively adjusting 
the parameters of the tolerance window based on the most recent successful 
tentative match. The tentative matches (and correspondences) are accepted 
if the edit distance for those correspondences is smaller than any other 
correspondences. 

There are several approaches to converting minutia correspondence 
information to a matching score. One straightforward approach for comput- 
ing the score S is 




Figure 8.15 Bounding box and its adjustment. (From Jain, A., Hong, L., Pankanti, 
S., and Bolle, R., Proc. IEEE (Special Issue on Automated Biometrics), 85(9), 
1365-1388, ©IEEE, September 1997.) 



v _mM PQ M PQ 

m p m q 



( 8 . 1 ) 



where M PQ is the number of corresponding minutiae, and M P and M Q are 
the total number of minutiae in template and test fingerprints, respectively. 
In some matchers, the total number of minutiae [M P and M Q in Equation 
(8.1)] is not used. After the correspondence is determined, an overall bound- 
ing box only for corresponding test and template minutiae is computed. The 
matching score S B is then computed as: 



s _ 100 M pq M pq 
B M pb M Qb 



( 8 . 2 ) 



where M PQ is the number of corresponding minutiae, and M Ph and M Qb are 
the number of minutiae in the overall bounding boxes computed for template 
and test fingerprints, respectively. Often, different normalizations are used 



S'* 




Figure 8.16 Fingerprinting matching: (a) Matching two impressions of the same 
finger, matching score = 49; (b) matching fingerprints from two different fingers, 
matching score = 4. 



for different counts of the total number of minutiae. The matching score 
when matching two impressions of the same finger is expected to be higher 
than when matching two fingerprints from different fingers (Figure 8.16). 

Due to space limitations, other important classes of fingerprint matchers 
based on topological (ridge connectivity) information are not included here; 
however, readers are referred to the literature 53,54 for related information. 




Fingerprint Enhancement 



The performance of a fingerprint feature extraction and image matching 
algorithm relies critically on the quality of the input fingerprint images. The 
ridge structures in poor-quality fingerprint images are not always well 
defined, and hence cannot be correctly detected. This leads to the following 
problems: (1) a significant number of spurious minutiae may be created, 
(2) a large percentage of genuine minutiae may be ignored, and (3) large 
errors in minutiae localization (position and orientation) may be introduced. 
To ensure that the performance of the minutiae extraction algorithm will be 
robust with respect to the quality of fingerprint images, an enhancement 
algorithm that can improve the clarity of the ridge structures is necessary. 
Traditionally, forensic applications have been the biggest end users of finger- 
print enhancement algorithms because the important ridge details are fre- 
quently obliterated in the latent fingerprints lifted from a crime scene. Over- 
inking, under-inking, imperfect friction skin contact, fingerprint smudges 
left from previous live-scan acquisitions, adverse imaging conditions, and 
improper imaging geometry/optics are some of the systematic reasons for 
poor-quality fingerprint images. It is widely acknowledged that at least 2 to 
5% of the target population have poor-quality fingerprints: fingerprints that 
cannot be reliably processed using automatic image processing methods. We 
suspect this fraction is even higher in reality when the target population 
consists of (1) older people, (2) people who suffer routine finger injuries in 
their occupation, (3) people living in dry weather conditions or having skin 
problems, and (4) people who have poor fingerprints due to genetic 
attributes. With the increasing demand for cheaper and more compact fin- 
gerprint scanners, fingerprint verification software cannot afford the luxury 
of assuming good-quality fingerprints obtained from the optical scanner. The 
cheaper and more compact semiconductor sensors not only offer smaller 
scan area but also typically poor-quality fingerprints. 

Fingerprint enhancement approaches 55 ' 58 often employ frequency 
domain techniques 56,58,59 and are computationally demanding. In a small local 
neighborhood, the ridges and furrows approximately form a two-dimen- 
sional sinusoidal wave along the direction orthogonal to local ridge orienta- 
tion. Thus, the ridges and furrows in a small local neighborhood have well- 
defined local frequency and orientation properties. The common approaches 
employ bandpass filters that model the frequency domain characteristics of 
a good-quality fingerprint image. The poor-quality fingerprint image is pro- 
cessed using the filter to block the extraneous noise and pass the fingerprint 
signal. Some methods can estimate the orientation and/or frequency of ridges 
in each block in the fingerprint image and adaptively tune the filter charac- 
teristics to match the ridge characteristics. 




u 





Figure 8.17 An even-symmetric Gabor filter: (a) Gabor filter tuned to 60 
cycles/width and 0° orientation; (b) corresponding modulation transfer function 
(MTF). (From Hong, L., Automatic Personal Identification Using Fingerprints, 
Ph.D. thesis, 1998.) 

One typical variation of this theme segments the image into non-over- 
lapping square blocks of width larger than the average inter-ridge distance. 
Using a bank of directional bandpass filters, each filter generating a strong 
response indicates the dominant direction of the ridge flow in the finger in 
the given block. The resulting orientation information is more accurate, 
leading to more reliable features. A single block direction can never truly 
represent the directions of all the ridges in the block and may consequently 
introduce filter artifacts. One common directional filter used for fingerprint 
enhancement is the Gabor filter. 60 Gabor filters (see Figure 8.17) have both 
frequency-selective and orientation-selective properties. For example, a prop- 
erly tuned Gabor filter will pass only fingerprint ridges of certain spatial 
frequency flowing in a certain specific direction. Typically, in a 500 dpi, 512 
x 512 fingerprint image, a Gabor filter with u 0 = 60 cycles per image width 
(height), the radial bandwidth of 2.5 octaves, and orientation 0 models the 
fingerprint ridges flowing in the direction 0 + n/2. 



Input Image 




Figure 8.18 Fingerprint enhancement algorithm. (From Hong, L., Automatic 
Personal Identification Using Fingerprints, Ph.D. thesis, 1998. With permission, 
fain, A.K. and Pankanti, S., Handbook for Image and Video Processing, Bovik, 
A., Ed., ©Academic Press, April 2000.) 

A novel approach to fingerprint enhancement proposed by Hong et al. 10 
(see Figure 8.18) is summarized here. It decomposes the given fingerprint 
image into several component images using a bank of directional Gabor 





bandpass filters and extracts ridges from each of the filtered bandpass 
images. 9 By integrating information from the sets of ridges extracted from 
filtered images, the enhancement algorithm infers the region of fingerprint 
where there is sufficient information available for enhancement (recoverable 
region) and estimates a coarse-level ridge map for the recoverable region. 
The information integration is based on the observation that genuine ridges 
in a region evoke a strong response in the feature images extracted from the 
filters oriented in the direction parallel to the ridge direction in that region 
and at most a weak response from the filters oriented in the direction orthog- 
onal to the ridge direction in that region. The resulting coarse ridge map 
consists of the ridges extracted from each filtered image which are mutually 
consistent; portions of the image where the ridge information is consistent 
across the filtered images constitute recoverable regions. The orientation field 
estimated from the coarse ridge map is more reliable than the orientation 
estimation from the input fingerprint image. After the orientation field is 
obtained, the fingerprint image can then be adaptively enhanced using the 
local orientation information. Typically, given the local orientation 0 at a 
pixel (x,y), the enhanced image pixel is chosen to be pixel (x, y) of the Gabor 
filter that has orientation 0. When Gabor filter with orientation 0 is not 
available, the enhanced pixel (x, y) can be linearly interpolated from the two 
Gabor filters with orientations closest to 0. The interpolation is computa- 
tionally efficient because the filtered images are already available during the 
previous stages of enhancement and it produces good results. 

Examples of fingerprint image enhancement are shown in Figure 8.19. 
An example illustrating the results of the minutiae extraction algorithm on 
a noisy input image and its enhanced counterpart are shown in Figure 8.20. 
The improvement in matching performance by incorporating image 
enhancement module was evaluated using the fingerprint matcher described 
in the previous chapter section. Figure 8.21 shows the ROC curves for the 
matcher that were obtained with and without image enhancement module 
on a database consisting of 700 fingerprint images of 70 individuals (10 
fingerprints per finger per individual). It is clear that the image enhancement 
has improved the performance of the matcher over this database. 



Large-Scale Systems Issues 

Typically, in a large-scale identification problem, given a fingerprint and a 
large database of fingerprints (e.g., millions), one would like to find out 
whether any one of the prints in the database matches the given fingerprint. 
A straightforward solution to this problem involves matching the given fin- 
gerprint with each fingerprint in the database. However, in this approach, 



the expected number of matches required to solve the identification problem 
increases linearly with the database size. It is therefore desirable to find more 
efficient solutions to the identification problem. 

There have been two primary approaches to make the identification 
searches more efficient. In the first approach, the database is organized so that 
certain matches can be ruled out based on the information extrinsic/intrinsic 
to the fingerprints. When the number of necessary matches is reduced based 
on the information extrinsic to the fingerprints, the solution is commonly 
referred to as filtering. For example, the database can be presegmented based 
on information about sex, race, age, and other bio-/geographical information 
related to the individual. In binning, a fingerprint’s intrinsic information 
(e.g., fingerprint class) is used to reduce the number of matches. 61 

The percentage of the total database to be scanned, on average, for each 
search is called the “penetration coefficient,” P, which can be defined as the 
ratio of the expected number of comparisons required for a single input 
image to the total number of prints in the entire database. Based on published 
results, we believe that binning can achieve a penetration coefficient of about 
50%. The second approach for making the search more efficient is to reduce 
the effective time given for each match. Given a matching algorithm, the 
effective time per match can be reduced by directly implementing the entire 
algorithm or components of it in special hardware. The other method of 
reducing the effective time per match is by parallelizing the matches, that is, 
using multiple processors and assigning a fraction of the matches to each 
processor. Some vendors have resorted to optical computing 41 to achieve a 
very high matching throughput. 

Scalability of accuracy performance of a large-scale identification system 
is a more formidable challenge than its speed performance. If the accuracy 
performance associated with matching each pair of fingerprints (e.g., verifi- 
cation accuracy) is characterized by false accept (FAR,) and false reject ( FRR v ) 
rates, the identification accuracy performance of the system with n records 
in the database (one per identity) can then be expressed as: 

FRR j = FRR v x FCR (8.3) 

FAR t = 1 - (l - FAR y ) nXP (8.4) 

under the underlying assumptions that (1) the outcome of each match is an 
independent event, (2) all the records in the database are correctly classified, 
(3) FCR is the probability of falsely classifying (binning) the given fingerprint 
into a wrong bin, and (4) the misclassification and mismatching events are 
independent. 




Figure 8.19 Examples of enhancement results: (a) and (c) are the input images; 
(b) and (d) show enhanced recoverable regions superimposed on the corresponding 
input images. 





Figure 8.19 (continued) 





(a) 



(b) 



s 

V 


s s 
^ \ 
OS '* 


bJ Ni 


v ^ s 


\ 






- \ 


\ \ v 




\ 


- **V7 


; 


1 





(c) 



Figure 8.20 Fingerprint enhancement results: (a) a poor-quality fingerprint; (b) 
minutia extracted without image enhancement; and (c) minutiae extracted after 
image enhancement. (From Hong, L. ( Automatic Personal Identification Using 
Fingerprints, Ph.D. thesis, 1998). 

A significant implication of the above accuracy equations is that the false 
accept rates of the identification deteriorate as a function of the size of the 
database (see Figure 8.22). Consequently, an effective identification system 
requires a very accurate matcher. 



System Evaluation 



Given a fingerprint matcher, one would like to assess its accuracy and speed 
performance in a realistic setting. This chapter section primarily deals with 
accuracy performance evaluation issues. 






ioL 



o l i i i i I 

10' 3 10‘ 2 10' 1 10 ° 10 1 10 2 
False Acceotance Rate (%) 

Figure 8.21 Performance improvement due to fingerprint enhancement algo- 
rithm. (From Hong, L., Automatic Personal Identification Using Fingerprints, 
Ph.D. thesis, 1998.) 




Figure 8.22 False acceptance error rates of verification (matcher) and identifi- 
cation systems. For example, a matcher that can match with a false acceptance 
error rate (FAR) of 1CH and a classifier with a penetration ratio (P) of 0.5 could 
typically result in an identification system (database population of 14,000 distinct 
fingers, 1 finger per individual) with a false acceptance error rate of approximately 
0.5. That is, the likelihood of the system determining a match from an arbitrary 
input fingerprint matching one of the 14,000 (actually, only half of them because 
of the classifier penetration ratio) fingerprints is 0.5. 

Given two fingerprints, a decision made by a fingerprint identification 
system is either a “match” or a “no-match.” For each type of decision, there 
are two possibilities: either the decision reflects the true state of the nature 






or otherwise. Therefore, there are a total of four possible outcomes: (1) a 
genuine (mated) fingerprint pair is accepted as a “match,” (2) a genuine 
fingerprint mated pair is rejected as “non-match,” (3) a non-mated finger- 
print pair (also called an impostor) is rejected as a “non-match,” and (4) an 
impostor is accepted as a “match” by the system. Outcomes (1) and (3) are 
correct, whereas (2) and (4) are incorrect. Thus, probabilities of a matcher 
committing false accept (or false match) and false reject (false non-match) 
errors are two necessary components to characterize the accuracy perfor- 
mance of a system. Note that false accept and false reject error rates are related 
to each other through the score threshold parameter determined by the 
system operating point. Further, it is widely acknowledged 62 that false 
accept/reject error rates at a single operating point do not provide sufficient 
information for system accuracy performance characterization; it is recom- 
mended that a curve, called ROC, describing the false accept/reject error rates 
at all possible score thresholds be plotted for a comprehensive perspective of 
the system accuracy, and this information provides a useful basis for system 
evaluation and comparison. 

To generate an ROC, a set of mated fingerprint pairs (e.g., a sample of 
genuine distribution) and a set of non-matching fingerprint pairs (e.g., a 
sample of impostor distribution) is necessary. The matcher scores resulting 
from mated fingerprint pairs are used to generate the genuine score proba- 
bility distribution, and the scores from non-mated fingerprint pairs are used 
to generate the impostor score probability distribution. Given a threshold 
score T, impostor scores larger than T contribute to the false accept error 
and the corresponding area under the impostor distribution curve quantifies 
the false accept error at that threshold (see Figure 8.23). Similarly, genuine 
scores smaller than T contribute to the false reject error and the correspond- 
ing area under the genuine distribution quantifies the false reject error at 
that threshold. 

For any performance metric to be able to precisely generalize to the entire 
population of interest, the test data should (1) be representative of the pop- 
ulation and (2) contain enough samples from each category of the popula- 
tion. The samples are collected so that the method of sensing and the method 
of presentation of the finger closely correspond to those in the real situations. 
Fingerprint images collected in a very controlled and non-realistic environ- 
ment provide overly optimistic results that do not generalize well in practice. 
Typically, the collected database has a significant number of non-mated pairs 
but lacks a sufficient number of mated paired samples. Further, the collection 
of two fingerprint impressions comprising a sample mated pair should be 
separated by a sufficient time period. Different applications, depending on 
whether the subjects are cooperative, and habituated, whether the target 
population is benevolent or subversive, may require a completely different 




Figure 8.23 Probability distributions of matcher scores from genuine mated and 
impostor fingerprint pairs. FRR and FAR denote the false reject and false accept 
error rates, respectively. 

sample set. Finally, the system may have to be tuned to peculiarities of the 
sample data (without overtuning it to arrive at optimistic error rate esti- 
mates). Techniques such as data sequestering 63 may be necessary to avoid 
overtuning the system. 

In principle, one can use the false (impostor) acceptance rate (FAR), the 
false (genuine individual) reject rate (FRR) at a single operating point, and 
the equal error rate (EER)* to indicate the identification accuracy of a bio- 
metric system. 64,65 In practice, these performance metrics can only be esti- 
mated from empirical data and the estimates of the performance are 
dependent on the fingerprint database used in the experiments. Therefore, 
they are meaningful only for a specific database in a specific test environment. 
For example, the performance of a biometric system as claimed by its man- 
ufacturer had an FRR of 0.3% and an FAR of 0.1%. An independent test by 
the Sandia National Laboratory found that the same system had an FRR of 
25% with an unknown FAR. 66 To provide a more reliable assessment of a 
biometric system, some more descriptive measures of performance are nec- 
essary. Receiver operating characteristic curve (ROC) is one such descriptive 
measure of performance (see Figure 8.21). 



* Equal error rate is defined as the error rate value where FAR and FRR are equal. 



Conclusions and Future Prospects 



Fingerprint-based personal identification is an important biometric tech- 
nique with many current and emerging applications. This chapter has pro- 
vided an overveiw of fingerprint-based personal identification, including an 
outline of some of the important issues involved in the design of fingerprint- 
based identification systems and algorithms for fingerprint feature extraction, 
enhancement, matching, and classification. A brief summary of the perfor- 
mance of these algorithms was also provided, in addition to a discussion of 
issues related to fingerprint representation, fingerprint identification system 
architecture, and performance evaluation. 

Fingerprint-based identification has come a long way since its inception 
more than 100 years ago. The first primitive scanners designed by Cornell 
Aeronautical Lab/North American Aviation Inc. were unwieldy beasts with 
many problems as compared to sleek, inexpensive, and relatively miniscule 
semiconductor sensors. Over the past few decades, research and active use 
of fingerprint matching and indexing have also advanced our understanding 
of individuality information in fingerprints and efficient ways of processing 
this information. Increasingly inexpensive computing power, cheap finger- 
print sensors, and the demand for security/ efficiency/convenience have led 
to the viability of fingerprint matching information for everyday positive 
person identification in recent years. 

There is a popular misconception that automatic fingerprint matching 
is a fully solved problem because it was one of the first applications of 
automatic pattern recognition. Despite notions to the contrary, there are a 
number of challenges that remain to be overcome in designing a completely 
automatic and reliable fingerprint matcher, especially when images are of 
poor quality as in the case of latent prints. Although automatic systems are 
successful, the level of sophistication of automatic systems in matching fin- 
gerprints today cannot rival that of a dedicated, well-trained fingerprint 
expert. Still, automatic fingerprint matching systems offer a reliable, rapid, 
consistent, and cost-effective solution in a number of traditional and newly 
emerging applications. The performance of various stages of an identification 
system, including feature extraction, classification, and minutiae matching, 
do not degrade gracefully with a deterioration in the quality of the finger- 
prints. Most of these deficiencies in the existing automatic identification systems 
are overcome by having an expert interact with the system to compensate for 
the intermediate errors. As mentioned, significant research appears to be nec- 
essary to enable us to develop feature extraction systems that can reliably and 
consistently extract a diverse set of features that provide rich information com- 
parable to those commonly used by the fingerprint experts. 




In most pattern recognition applications (e.g., OCR), the best-perform- 
ing commercial systems use a combination of matchers, matching strategies, 
and representations. There is limited work being done in combining multiple 
fingerprint matchers ; 67,68 more research/ evaluation of such techniques is needed. 
The proprietary set of features used by the system vendors and a lack of a 
meaningful information exchange standard makes it difficult — if not impos- 
sible — for law enforcement agencies to leverage the complementary strengths 
of different commercial systems. Multi-modal (e.g., multiple biometrics) 
systems provably deliver better performance than any single constituent bio- 
metric . 69 The lack of standardization also poses challenges in integrating 
different biometrics (e.g., face and finger , 70 finger and speech 71 ) in the context 
of forensic identification systems. 

On a more speculative note, perhaps, using human intuition-based man- 
ual fingerprint identification systems may not be the most appropriate basis for 
the design of automatic fingerprint identification systems; there may be a need 
for exploring radically different features 40,52 rich in discriminatory information, 
radically different methods of fingerprint matching , 51 and more ingenious 
methods for combining fingerprint matching and classification that are ame- 
nable to automation. 

Only a few years ago it seemed as if the interest in fingerprint matching 
research was waning. As mentioned, due to increasing identity fraud in our 
society, there is a growing need for positive person identification. Cheap 
fingerprint sensors, the easy availability of inexpensive computing power, and 
our (relatively better) understanding of individuality information in finger- 
prints (compared to other biometrics) have attracted significant commercial 
interest in fingerprint-based personal identification. Consequently, dozens of 
fingerprint identification vendors have mushroomed in the past few years. 
Pervasive embedded applications of fingerprint-based identification (e.g., in 
a smart card or in a cell phone) may not be far behind. The authors strongly 
believe that higher visibility of (and liability from) performance limitations of 
commercial fingerprint identification applications will fuel a much stronger 
research interest in some of the most difficult research problems in fingerprint 
based identification. Some of these difficult problems will entail solving not only 
the hard core pattern recognition challenges, but also confronting the very 
challenging system engineering issues related to security and privacy. 



Acknowledgments 

We are grateful to Prof. Jay Siegel, Department of Criminal Justice, Mich- 
igan State University, for his detailed comments and editorial suggestions. 
Thanks also to Chris Brislawn, Los Alamos National Laboratory, for sharing 




WSQ-related illustrations (Figure 8.3). We appreciate the help of Lin Hong, 
Salil Prabhakar, Arun Ross, and Dan Gutchess in preparing this manuscript. 



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Measurement of 
Fingerprint Individuality 



9 



DAVID A. STONEY 



Contents 



Introduction 

Standards in Fingerprint Identification 
The Laws or Premises Underlying Fingerprint Identifications 
The Basis for Absolute Identification 
Limitations of Traditional Points of Comparison 
Fingerprint Individuality Models 
Galton Model (1892) 

Description of the Galton Model 
Discussion of the Galton Model 
The Henry-Balthazard Models (1900-1943) 

Description of the Henry-Balthazard Models 
Henry Model (1900) 

Balthazard Model (1911) 

Bose Model (1917) 

Wentworth and Wilder Model (1918) 

Cummins and Midlo Model (1943) 

Gupta Model (1968) 

Discussion of the Henry-Balthazard Models 
Roxburgh Model (1933) 

Description of the Roxburgh Model 
Discussion of the Roxburgh Model 
Amy Model (1946-1948) 

Description of the Amy Model 
Variability in Minutia Type 
Variation in Number and Position of Minutiae 
Probability for a Particular Minutiae Configuration 
Chance of False Association 

Final Equation for the Chance of Random Association 
Discussion of the Amy Model 



Trauring Model (1963) 

Description of the Trauring Model 
Discussion of the Trauring Model 
Kingston Model (1964) 

Description of the Kingston Model 

Probability of the Observed Number of Minutiae 
Probability of the Observed Positioning of Minutiae 
Probability of the Observed Minutiae Types 
Overall Probability of a Given Configuration 
Chances of False Association 
Discussion of the Kingston Model 
Osterburg Model (1977-1980) 

Description of the Osterburg Model 
Discussion of the Osterburg Model 
Stoney and Thornton Model (1985-1989) 

Model Features Proposed by Stoney and Thornton 

Ridge Structure and Description of Minutia Location 
Description of Minutia Distribution 
Orientation of Minutiae 
Variation in Minutia Type 
Variation among Prints from the Same Source 
Number of Positionings and Comparisons 
Description of the Stoney and Thornton Model 
Minutia Description and Survey 
Statistical Analysis and Findings 
Discussion of the Stoney and Thornton Model 
Champod and Margot Model (1995-1996) 

Description of the Champod and Margot Model 
Experimental Design 
Statistical Analysis and Findings 
Conclusion 

Discussion of the Champod and Margot Model 
Meagher, Budowle, and Ziesig Model (1999) 

Description of the Meagher, Budowle, and Ziesig Model 

The First Experiment, Based on Inter-comparing Records 
of Rolled Fingerprints 

The Second Experiment, Based on Comparing Subsets 
of the Records with the Same Complete Records 
Discussion of the Meagher, Budowle, and Ziesig Model 
Conclusions 
References 



Introduction 



This chapter examines the underlying statistical basis for fingerprint com- 
parisons and reviews the efforts that have been made to measure friction 
ridge variability as it relates to forensic comparison and identification of 
fingerprints. 

This chapter does not consider the foundational information that sup- 
ports the practice of fingerprint identification. That is, the chapter does not 
review the embryology, comparative anatomy, and genetics of friction ridge 
skin. These well- developed areas of study do contribute essential information 
that establishes the feasibility and utility of fingerprint identifications, but 
they do not provide criteria for concluding that two fingerprints were made 
by the same finger. Neither does the long-standing practice and effectiveness 
of fingerprint evidence provide such criteria. 

This chapter is specifically concerned with the question: How much 
correspondence between two fingerprints is sufficient to conclude that they 
were both made by the same finger? The amount of correspondence has two 
dimensions: quantity and quality. Quantity itself includes two aspects. The 
first is how much of the skin surface is represented in the comparison; and 
the second is how many (and what kind of) details make up the correspon- 
dence. The dimension of quality in a fingerprint correspondence is deter- 
mined by how clearly and accurately the skin surface is represented in the 
two prints. 

An adequate answer to the question posed in the preceding paragraph 
is not currently available. The best answer at present to the question, “How 
much is enough?” is that this is up to the individual expert fingerprint 
examiner to determine, based on that examiner’s training, skill, and experi- 
ence . 1 Thus, we have an ill-defined, flexible, and explicitly subjective criterion 
for establishing a fingerprint identification. The need for a standard, objective 
criterion has itself been controversial because subjective methods have been 
so universally effective and accepted for so long. Even admitting the need, 
there is considerable difficulty in defining meaningful measurements for 
quality and quantity in fingerprint comparisons. This difficulty will become 
apparent in this review of the efforts that have been made. 

The chapter begins by looking at the foundational aspects and standards 
that are in place regarding the making of a fingerprint identification; that is, the 
criteria for establishing that two fingerprints were made by the same finger. 

Standards in Fingerprint Identification 

Any unbiased, intelligent assessment of fingerprint identification practices 
today reveals that there are, in reality, no standards. That is, the amount of